the importance of variable lateral connectivity ...

RIVER RESEARCH AND APPLICATIONS

River Res. Applic. 28: 1189–1199 (2012) Published online 7 April 2011 in Wiley Online Library (wileyonlinelibrary.com) DOI: 10.1002/rra.1498

THE IMPORTANCE OF VARIABLE LATERAL CONNECTIVITY BETWEEN ARTIFICIAL FLOODPLAIN WATERBODIES AND RIVER CHANNELS J. D. BOLLAND,a,b* A. D. NUNN,a M. C. LUCASb and I. G. COWXa b

a University of Hull International Fisheries Institute, Hull, UK School of Biological and Biomedical Sciences, Durham University, Durham, UK

ABSTRACT The rehabilitation of lowland rivers subjected to channelization and artificial levee construction should attempt to improve habitat heterogeneity and diversity of floodplain hydrological connectivity. However, rehabilitation efforts rarely consider the importance of variable lateral hydrological connectivity between floodplain waterbodies and main river channels (ranging from those permanently connected to those temporarily connected during river level rises), instead focusing on increasing individual floodplain waterbody connectivity. This study investigated the young‐of‐the‐year (YoY) fish communities in 10 artificial floodplain waterbodies of variable hydrological connectivity with the river Trent, England, between May and November 2006, inclusive. Floodplain waterbody connectivity to the main river was positively correlated with the number of species captured (alpha diversity), Shannon–Wiener diversity, Margalef’s species richness index and the relative abundance of rheophilic species and negatively correlated with species turnover (beta diversity). YoY fish communities in poorly connected water bodies were most dissimilar to riverine communities. The results demonstrate the importance of variable lateral connectivity between artificial floodplain waterbodies and main river channels when rehabilitating lowland river fish communities. Copyright © 2011 John Wiley & Sons, Ltd. key words: flood; reproductive guild; spatial heterogeneity; refuge; rehabilitation Received 21 May 2010; Revised 5 January 2011; Accepted 25 January 2011

INTRODUCTION Natural floodplain rivers have habitats along the gradient of lateral connectivity (flow of energy, matter and organisms; Ward et al., 2002), ranging from those permanently connected to those temporarily connected to the main river during river level rises (Amoros et al., 1982). Consequently, fish communities in lowland riverine ecosystems are composed of rheophilic (require flowing water to spawn), eurytopic (habitat generalists) and limnophilic (found in stagnant and strongly vegetated floodplain waterbodies) fish species guilds (Copp et al., 1991; Schiemer and Waidbacher, 1992; Welcomme et al., 2006) that contribute to the overall high species diversity (Copp, 1989). Flow regulation, channelization and artificial levee construction (Ward, 1998; Amoros and Bornette, 2002) often reduce rivers to single‐thread channels and impede lateral connectivity with their floodplains and lentic waters (Ward and Stanford, 1995; Cowx and Welcomme, 1998). Such activities incur enormous losses in fish spawning, production and nursery areas, which may cause reductions in overall abundance and

*Correspondence to: J. D. Bolland, University of Hull International Fisheries Institute, Cottingham Road, Hull, HU6 7RX, UK. E‐mail: [email protected]

Copyright © 2011 John Wiley & Sons, Ltd.

species diversity and culminate in an increased number of threatened fish taxa (Schiemer and Waidbacher, 1992; Aarts and Nienhuis, 2003). Reductions in landscape connectivity, ecological functioning and ecosystem biodiversity have driven initiatives to improve the ecological status of rivers, for example, the European Union, Water Framework Directive (2000/60/EEC), and to protect biological diversity, for example, the Habitats Directive (92/43/EEC) and Agenda 21 of the Rio Convention and the Convention of Biological Diversity. Achieving good ecological status or potential of degraded rivers involves rehabilitation of the functional integrity (hydrological connectivity and habitat heterogeneity) and ecological processes of the river–floodplain ecosystem, which are linked to high levels of biological diversity (Ward, 1998; Schiemer et al., 1999; Ward et al., 1999). However, rehabilitation schemes rarely consider the importance of variable lateral hydrological connectivity between floodplain waterbodies and main river channels. Instead, efforts are focused on increasing individual floodplain waterbody connectivity to the main channel in an attempt to maintain riverine fish community structure. For example, several studies documented the importance of permanently connected, artificial floodplain waterbodies as spawning, feeding, nursery (growth) and refuge areas (Sabo and Kelso, 1991; Neumann et al., 1994; Staas and Neumann, 1996; Pinder,

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J. D. BOLLAND ET AL.

1997; Simons et al., 2001; Grift et al., 2003; Jurajda et al., 2004; Nunn et al., 2007). In many of these studies, isolated floodplain waterbodies were connected to the main river channel, invariably at the expense of distinct communities dependent on the lentic environment within them. Consequently, riverine ecosystem rehabilitation should account for variable lateral connectivity between a range of floodplain waterbodies and the main river. The aim of this study was to evaluate the importance of variable connectivity between artificial floodplain waterbodies on the lowland section of the main stem of the river Trent, England, for rehabilitating the river–floodplain ecosystem. Specifically, the study compared young‐of‐the‐year fish (YoY, age 0+) species diversity, richness and composition across the gradient of floodplain connectivity and assessed the impact of artificial floodplain waterbodies on the overall community structure. The results are discussed with consideration of the ecological requirements of lowland river fishes and the overriding processes influencing fish presence and distribution, including floods and people.

STUDY AREA The study was carried out on the lower river Trent, England. The river Trent is the third longest river in the UK (298 km), has a catchment area of 10 500 km2 and a long‐term mean discharge of 84 m3 s−1. Historically, the Trent was geomorphically active and prone to meander, but its channel has remained relatively stable in recent times, particularly since regulation of the river began approximately 300 years ago (Large and Petts, 1996; Large and Prach, 1998). Currently, the lower Trent is channelized in many areas and impounded by a number of large weirs and sluices. Overbank flooding occurs relatively infrequently because

of the regulated nature of the river. In some areas, water depths are artificially maintained for the transport of freight and pleasure craft by periodic dredging, and much of the floodplain has been claimed for urban development or agriculture. Since the mid‐1990s, attempts have been made to re‐establish the link between the lower reaches of the river and its floodplain by connecting a number of artificial waterbodies (e.g. flooded gravel quarries) (Nunn et al., 2007). The main aim of the restoration project was to increase the availability and diversity (spawning and nursery habitat, refuge from floods) of habitat for fishes, particularly the early developmental stages, with a view to enhancing fish recruitment success within the lower reaches of the river. MATERIALS AND METHODS Survey sites Assemblages of 0+ fishes were surveyed at five river (R1–R5; width = 75–100 m and maximum depth = 3–4 m) and 10 floodplain waterbody (F1–F10; Table I) sites (Figure 1). Connectivity varied between floodplain waterbodies, ranging from those permanently connected to the river by deep open channels to those connected only during river levels >1.5 m above the mean summer river level (Table I). Connectivity was ranked based on the width (m), depth (m) and length (m) of permanent connection or river level rise required for temporary connection. All permanently connected floodplain waterbodies were classed as more highly connected than temporary ones. Permanently connected floodplain sites with wide, deep and short connecting channels were ranked higher than those with shallow, narrow and long connecting channels using the simple metric of (channel width × depth) / channel length (Table I).

Table I. Details of river Trent floodplain waterbodies surveyed (ordered downstream to upstream) for 0+ fishes, including area (A, ha), maximum depth (Max. D, m), dimensions of connection channel (W, width; D, depth and L, length, m) or river level rise required for connection (m) and connectivity rank (see text for details) Site name

Dunham Lake Winthorpe Lake Binghams Pond Farndon Pond Marina Pond Marina Cut Cowlick Marina Thrumpton Pond Ully Gully Glazebrook Pond

Code

F1 F2 F3 F4 F5 F6 F7 F8 F9 F10


Dimensions

Connection channel

A (ha)

Max. D (m)

L × W × D (m)

River level rise (m)

Rank

2 5 2.5 0.8 3 3 1 0.5 1 1

3 4 3 2 3 3 3 1.5 1.5 4

— 50 × 2 × 1 40 × 2 × 1 30 × 2 × 0.4 — — 30 × 20 × 3 — 0.5 × 7 × 0.7 50 × 1.5 × 0.2

1.5 — — — 0.1 0.1 — 0.5 — —

10 4 3 5 7.5 7.5 2 9 1 6

River Res. Applic. 28: 1189–1199 (2012) DOI: 10.1002/rra

REHABILITATION OF FLOODPLAIN CONNECTIVITY

10 km

R1, F1 F2 F3 F4

Nottingham R2, F5, F6 F7 R3 R4 F9, F10

R5, F8

Birmingham

Figure 1. A map of England showing the location of the Trent

catchment and a more detailed catchment map showing five main river (R1–R5) and 10 floodplain waterbody (F1–F10) sampling sites.

Surveys of 0+ fishes At all river and floodplain sites, 0+ fishes were surveyed using a micromesh seine net (25 m long by 3 m deep, 3 mm hexagonal mesh; one haul per site on each occasion) that was set in a rectangle parallel to the bank by wading. Surveys were performed on 10 occasions, approximately fortnightly from May to July and monthly from August to November 2006, in daylight hours. In all cases, sampling was restricted to areas devoid of large woody debris, in water ≤1.5 m deep, where water velocity was slow and where 0+ fishes tend to aggregate. The seine net effectively captured 0+ fishes, including benthic species (e.g. gudgeon; Nunn et al., 2007) and larvae as small as 5 mm, although its efficiency was lower for fish smaller than ~15 mm (Cowx et al., 2001). Captured fish were identified to species (Pinder, 2001) and measured for standard length (nearest millimetre). Data analysis The number of species caught at each site (all surveys between May and November combined; alpha diversity), Copyright © 2011 John Wiley & Sons, Ltd.

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the turnover of species between each floodplain waterbody and the main river (beta diversity, Whittaker’s measure) and the overall number of species caught from all sites (gamma diversity) were calculated (Magurran, 1988). Whittaker’s measure of beta diversity (βW) was calculated as βW = (S/α) − 1, where S is the total number of species present along the river–floodplain gradient and α is the average of the total number of species caught in each floodplain waterbody and the main river (Magurran, 1988). Relative abundance, frequency of occurrence, Shannon– Wiener diversity index (H′) and Margalef’s species richness index (d) (Washington, 1984) were calculated from all the surveys at each site. The relative abundance of a species was defined as the total number of a particular species caught, expressed as a percentage of the total number of all 0+ fishes caught in all the surveys at each site. The frequency of occurrence of a given species at each site was defined as the number of surveys in which the species was captured, expressed as a percentage of the total number of surveys carried out. Species composition of 0+ fish catches was analysed for all sites using the graphical method of Costello (1990), as modified by Amundsen et al. (1996), by plotting species‐ specific abundance against frequency of occurrence for all species caught at each site. Species‐specific abundance was defined as the percentage contribution of a species relative to the total catch, in only those surveys where that particular species was captured. Points located at the lower left corner of the graph represent species that occurred infrequently and in low numbers (rare species), those located at the lower right are species that occurred in most surveys but in only small numbers and those located at the upper right are those that frequently occurred in large numbers (dominant species). Note, data points may overlap, and for clarity, only species that occurred frequently (>60%) or in large numbers (>20%) are labelled. Spearman rank correlation was used to test the null hypotheses that floodplain waterbody connectivity was not significantly correlated with alpha diversity, beta diversity, H′ and d of the 0+ fish communities and the relative abundance of rheophilic species. Rheophilic fish species require flowing water to spawn (Welcomme et al., 2006) and, as such, were used as an indicator of lateral movements of 0+ fishes from the main river. Statistical analyses were carried out using SPSS (version 15.0; SPSS Inc., Chicago, IL, USA) with a significance level of α = 0.05. To investigate the similarity in 0+ fish species composition between sites, a Bray–Curtis similarity matrix (Bray and Curtis, 1957) was calculated using mean percentages of each 0+ fish species and presented as a dendrogram using hierarchical agglomerative clustering (complete linkage). The index ranges from 0 (no species in common) to 1 (identical samples), and a similarity profile (SIMPROF) test River Res. Applic. 28: 1189–1199 (2012) DOI: 10.1002/rra

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Eurytopic

Number of species

10

5

0 100

(b) 75

50

25

F1

F8

F6

F5

F4

F10

F2

F3

F7

F9

R5

R4

R3

0

R2

More than 555 700 specimens and a total of 25 fish species (gamma diversity) were captured during the study period. Of these, 22 species (almost 220 000 individuals) were caught from main river sites and 22 species (>336 000 individuals) were caught from floodplain waterbodies (Table II). The number of species captured in individual floodplain waterbodies (alpha diversity) was positively correlated with hydrological connectivity (Spearman rank: r = 0.731, n = 10, p = 0.016). Furthermore, the diversity indices d (Spearman rank: r = 0.681, n = 10, p = 0.030; Table III) and H′ both declined with decreasing connectivity to the main channel, although the trend for H′ was not significant (Spearman rank: r = 0.377, n = 10, p = 0.283). Beta diversity increased with increasing isolation of the floodplain waterbody, as similarity with the species composition in the main river declined (Spearman rank: r = −0.688, n = 10, p = 0.028). Overall, catches from floodplain waterbodies were dominated by eurytopic species (Figure 2); specifically, roach [Rutilus rutilus (L.)—37%] and perch (Perca fluviatilis L.—22%) were the most abundant and also occurred most frequently (roach = 72% and perch = 61%; Table II). Three limnophilic species {10‐spined stickleback [Pungitius pungitius (L.)], rudd [Scardinius erythrophthalmus (L.)] and tench [Tinca tinca (L.)]} occurred exclusively in floodplain waterbodies. Rheophilic species that dominated the main river catches (Figure 2) were captured in all floodplain waterbodies (Table II), and their relative abundance (Figure 2) was positively correlated with floodplain waterbody connectivity (Spearman rank: r = 0.839, n = 10, p = 0.002). Rheophilic species were only caught in the four temporarily connected floodplain waterbodies (F1, F5, F6 and F8; Table II) after a flood at the end of May 2006. The 0+ fish community structure varied between floodplain waterbodies (Figure 3) and between main river sites (Figure 4), but three main cluster groups were identified

Rheophilic

15

R1

RESULTS

Limnophilic

(a)

Percent abundance.

was used to ascertain whether clusters of sites were statistically significantly similar with one another (Clarke et al., 2008). SIMPROF is a permutation test of the null hypothesis that a specified set of samples, which are not a priori divided into groups, do not differ from each other in multivariate structure. In this process, tests are performed at every node of the completed dendrogram to provide objective stopping rules and identify whether groups being sub‐divided have significant internal structure (i.e. that samples in each group show evidence of multivariate pattern). To test the null hypothesis that there was no ordered sequence of species assemblage change with floodplain waterbody connectivity, a similarity matrix (RELATE) was performed (Somerfield et al., 2002).

Figure 2. Number (a) and percent abundance (b) of rheophilic,

eurytopic and limnophilic species captured from five main river sites (R1–R5) and 10 floodplain waterbodies (F1–F10; ordered from highly to poorly connected sites) on the river Trent. Flow preference classification according to Schiemer and Waidbacher (1992).

within the 0+ fish communities that were significantly similar [Figure 5(a)]. One group was dominated by dace [Leuciscus leuciscus (L.); R2, R3 and F7], one was dominated by roach, chub and dace (R1, R4, R5, F3 and F9) and the final group was dominated by roach and perch (F4, F5, F10, F2 and F6). F7, F3 and F9 were the most highly connected floodplain waterbodies and were grouped with main river sites. The two sites most isolated from the main river, F8 [three‐spined (Gasterosteus aculeatus L.) and 10‐spined sticklebacks] and F1 {carp (Cyprinus carpio L.) and bream [Abramis brama (L.)]}, were significantly dissimilar to all other sites [Figure 5(a)]. These cluster groups approximated the degree of floodplain waterbody connectivity, with poorly connected waterbodies containing 0+ fish communities most dissimilar to riverine communities [Figure 5(b)]. Furthermore, there was a significant ordered relationship of community change with floodplain waterbody connectivity (RELATE; global R = 0.472, p = 0.1%). River Res. Applic. 28: 1189–1199 (2012) DOI: 10.1002/rra


Barbel Carp Gudgeon

Bb Cc Gg

Barbus barbus (L.)

Cyprinus carpio L.

Gobio gobio (L.)

Tench

Rr Se Tt Ct

Rutilus rutilus (L.)

Scardinius erythrophthalmus (L.)

Tinca tinca (L.)

Cobitidae Cobitis taenia L.

Esox lucius L.

Esocidae

Barbatula barbatula (L.) El

Bt

Roach Rudd

Rs

Rhodeus sericeus (Pallas)

Balitoridae

Bitterling

Pp

Phoxinus phoxinus (L.)

Pike

Stone loach

Spined loach

Minnow

Dace

Leuciscus leuciscus (L.)

Chub

Lc Ll

Leuciscus cephalus (L.)

Eury

Rheo A

Rheo B

Limno

Limno

Eury

Limno

Rheo A

Rheo A

Rheo A

Rheo B

Eury

Rheo A

Eury

Eury

Bleak

Aa

Bream

Ab

Eury

Alburnus alburnus (L.)

R3

R4

R5

F9

F7

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

F2

F3

R2

pref. b R1

Site code

Flow

Silver bream

Vernacular name

Abramis brama (L.)

a

Aj

Ab.

Abramis bjoerkna (L.)

Cyprinidae

Species

Family

-

-

-

-

-

-

-

F4

-

-

-

-

-

-

-

-

-

F10

-

-

-

-

-

-

-

F5

-

-

-

-

-

-

-

-

F6

-

-

-

-

-

-

-

-

F1

(Continues)

-

-

-

-

-

-

-

-

F8

Table II. Relative abundance of 0+ fish captured from five main river sites (R1–R5) and 10 floodplain waterbodies (F1–F10; ordered from highly to poorly connected sites) on the river Trent


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River Res. Applic. 28: 1189–1199 (2012)

DOI: 10.1002/rra


Sl

Sander lucioperca (L.)

Pomatoschistus microps (Krøyer) Flounder

Rheo C

-

-

-

-

-

R1

-

-

-

-

-

R2

-

-

-

R3

-

-

-

-

R4

-

-

-

-

-

-

R5

-

-

-

-

-

F9

-

-

-

-

-

F7

-

-

-

-

-

-

F3

-

-

-

F2

Site code

-

-

-

-

F4

-

-

-

-

-

-

-

-

F10

-

-

-

-

-

-

F5

-

-

-

-

-

-

F6

-

-

-

-

-

-

F8

-

-

-

-

-

-

F1

Ab. = Species abbreviation. flow preference classification according to Schiemer and Waidbacher (1992): Rheo A = rheophilic A, Rheo B = rheophilic B, Eury = eurytopic and Limno = limnophilic.

Pf

Eury

Zander

Eury

Rheo A

Limno

Eury

Eury

Common goby

b

Rheo A

pref.

Flow

Perch

Ruffe

Bullhead

Three-spined stickleback Ten-spined stickleback

Brown/sea trout

Vernacular name

Dominant (> 75 %) Abundant (51-75 %) Frequent (26-50 %) Occasional (6-25 %) Infrequent (1-5 %) Rare (< 1 %) Not captured

-.

Key (percent frequency of occurrence and abundance)

b

a

Platichthys flesus (L.)

Pleuronectidae

Pm

Pf

Perca fluviatilis L.

Gobiidae

Gc

Gymnocephalus cernuus (L.)

Percidae

Cottus gobio L.

Cg

Pp

Pungitius pungitius (L.)

Cottidae

Ga

St

Ab.a

Gasterosteus aculeatus L.

Gasterosteidae

Salmo trutta L.

Salmonidae

Species

Family

Table II. (Continued)

1194 J. D. BOLLAND ET AL.

River Res. Applic. 28: 1189–1199 (2012)

DOI: 10.1002/rra

1195


100

100

F1

60

Pf

60

Cc

Ab

40

Gg Lc Aa

40

Ga

20

20

Rr

Pp

Ll

0

0 0 100

20

40

60

80

100

0 100

F3

20

40

60

80

100

F4

Rr

80

80 60

60

Gg Lc Aa Rr Gc Pf Ll

40 20

20

Pp 20

0 100

40

60

80

0 100

Lc

20

40

60

80

100

F6

Pf

20

0

0 60

Rr

40

20 40

Ll

60

Rr

40

20

Ll

80

60

0

Aa

0

100

Gg F5

80

Pf

40

0

Species -specific abundance ( )

F2

80

80

80

Aj Ll 0

100

20

40

60

80

100

100

100

F7

80

Ll

F8

80

Ga

60

60 40

Rr

Pf Lc

20 0 0

20

40

60

40

Rr

20

Pp

0

80

0

100

100

20

40

60

80

100

80

100

100

F9

80

F10

80

60

Gg

40

60

Aa

40

Rr

Lc Ll

20

Pp

Rr

Pf

20

Pf

0

0 0

20

40

60

80

100

0

20

40

60

Frequency of occurrence ( ) Figure 3. Costello plots demonstrating 0+ fish community structure at 10 floodplain waterbodies on the river Trent (see text for details).

Species name abbreviations are as in Table II.

DISCUSSION Natural river–floodplain ecosystems are characterized by aquatic and riparian habitats along the gradient of lateral Copyright © 2011 John Wiley & Sons, Ltd.

connectivity, which collectively contribute high levels of structural and biological diversity (Welcomme, 1979; Copp, 1989; Junk et al., 1989; Amoros and Petts, 1993; Amoros and Bornette, 2002). Lateral hydrological connectivity is River Res. Applic. 28: 1189–1199 (2012) DOI: 10.1002/rra

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100

R1

80 60

Ll

Lc Aa Gg

40 20

Rr Pf

0

Species -specific abundance ( )

0 100

20

40

60

80

100 100

R2

Ll

80 60

60

40

40

Pf

20

Rr

R3

80

Ll Rr Pf Lc

20

Gg

0

0 0 100

20

40

60

80

20

40

60

80

100

100

R4 Lc Aa Ab Gg Pf Gc

80 60 40 20

60

40

60

80

Lc

Ll Gg Aa

40

Rr Ll

0 20

R5

80

Rr

20

Pp 0

0

100

100

Pp

0 0

20

40

60

80

100

Frequency of occurrence ( ) Figure 4. Costello plots demonstrating 0+ fish community structure at five main river sites on the river Trent (see text for details). Species

name abbreviations are as in Table II.

the transfer of water between river channels and their floodplains, which influences the ease with which organisms, matter or energy traverse the ecotones between main rivers and floodplain waterbodies (Ward et al., 1999). The rehabilitation of degraded rivers should involve reinstating a range of lateral hydrological connectivity and thus the ecological processes of the river–floodplain

ecosystem (Ward, 1998; Schiemer et al., 1999; Ward et al., 1999; Morley et al., 2005). However, in human‐ modified river basins, restoration of aquatic habitats towards pristine conditions is considered a utopian view (Cowx and van Zyll de Jong, 2004). Therefore, recovery towards a ‘functional’ condition is usually the target (Cowx and van Zyll de Jong, 2004; Wolter, 2010), which is generally

Table III. Shannon–Wiener diversity index (H′) and Margalef’s species richness index (d) for all surveys from five main river sites (R1–R5) and 10 floodplain waterbodies (F1–F10; ordered from highly to poorly connected sites) and beta diversity (βW) between floodplain waterbodies and local river sampling sites on the river Trent Site code

d βW

R1 1.76

R2 0.94

R3 1.10

R4 1.92

R5 1.43

F9 1.52

F7 1.08

F3 1.96

F2 1.41

F4 0.63

F10 0.89

F5 1.10

F6 0.93

F8 1.03

F1 1.19

1.52

1.14

1.35

1.41

1.45

1.52

1.14

1.34

1.48

1.20

0.92

1.25

1.03

0.93

1.00

-

-

-

-

-

0.20

0.19

0.28

0.20

0.15

0.36

0.25

0.27

0.20

0.50




0

(a)

Similarity

20

40

60

F6

F1

F2

F8

F3

F5

F6

R4

F10

F2

R1

F4

F3

F9

R5

F7

R2

R4

10

R1

Connectivity rank

100

R3

80

F4 F10 F5

F8

F1

(b)

5

0 R2

R3

F7

R5

F9

Figure 5. Similarity (a) of 0+ fish species composition between five main river Trent (R) and 10 floodplain waterbodies (F) of variable connectivity (b). Significantly similar sites (SIMPROF) are identified in the main text. Note, low connectivity rank = highly connected. This figure is available in colour online at wileyonlinelibrary.com/journal/rra.

achieved by recreating floodplain habitats with a range of connectivity as typically observed in a natural riverscape (Cowx and Welcomme, 1998). Unfortunately, it is largely unknown if artificial floodplain waterbodies of variable connectivity ‘function’ naturally, thus replacing the habitat that was lost as a result of river engineering and flow regulation. The waterbodies investigated in this study ranged from those with permanent connection to those only temporarily connected during elevated river levels, a spectrum of connectivity comparable with a natural riverscape. Previous studies on unmodified river reaches have reported that fish species richness (Tockner et al., 1998) and alpha diversity (Ward et al., 1999) declined in floodplain waterbodies with increasing isolation from the main channel, whereas beta diversity increased (Ward et al., 1999). The findings followed similar trends, as floodplain waterbody connectivity to the main river was positively correlated with species richness and alpha diversity and negatively correlated with beta diversity. Hence, recreating functional habitats resulted in the recovery of 0+ fish populations towards a ‘normative’ condition. As the findings from this study compared favourably with near natural river reaches, the habitats appear to match the ecological requirements of lowland river fish species found in this region of the UK. In natural floodplains, eurytopic Copyright © 2011 John Wiley & Sons, Ltd.

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fishes perform spawning migrations from the main river into connected waterbodies, and 0+ fishes hatching in the main river (eurytopic and rheophilic) disperse into connected floodplain waterbodies to take advantage of abundant food resources and refuge from velocity (Hohausová, 2000; Borcherding et al., 2002; Hohausová et al., 2003; Nunn et al., 2007). In the river Trent, the proportion of rheophilic species in permanently connected floodplain waterbodies increased along the gradient of increasing connectivity, based presumably on the ability to disperse from their lotic spawning habitat in the main river. Three limnophilic species occurred exclusively in floodplain waterbodies, but there was no corresponding increase in relative abundance of limnophilic species, perhaps suggesting that the connectivity of the waterbodies to the main river is too high for these species to dominate. Despite this, 0+ fish community structure related approximately with floodplain waterbody connectivity, with poorly connected waterbodies containing distinct fish communities most dissimilar to riverine communities. Therefore, rehabilitation of the lowland river–floodplain ecosystems should account for variable levels of floodplain waterbody connectivity to ensure that the sequential shift in fish community composition from rheophilic to eurytopic to limnophilic fish species guilds is maintained (Copp et al., 1991; Schiemer and Waidbacher, 1992; Welcomme et al., 2006). Larval and juvenile fishes have poor swimming capabilities (Harvey, 1987); thus, the likelihood of surviving floods is greatly enhanced by occupying refuge areas of lower current velocity typically found in off‐channel waterbodies (Baras et al., 1995; Grift et al., 2003; Schiemer et al., 2004; Humphries et al., 2006). During the study, a flood at the end of May 2006 resulted in the lateral displacement of larval and juvenile fish (including rheophilic species) into four previously unconnected floodplain waterbodies, thus enabling them to take advantage of the previously isolated floodplain habitats for flow refuge, a finding consistent with studies elsewhere (Sedell et al., 1990; Molls and Neumann, 1994). Thus, floodplain waterbodies isolated from the main river at normal flows can support distinct fish communities while providing flow refuge to riverine fish species during flood events. Guidelines for holistic riverine ecosystem management implicitly state the necessity to restore spatio‐temporal diversity and functional integrity of the river–floodplain complex responsible for high levels of biological diversity (Ward 1998; Schiemer et al., 1999; Ward et al., 1999). This study identified that artificial floodplain waterbodies of variable connectivity create habitats that are functionally similar to natural lowland river–floodplain ecosystems; ‘normative’ 0+ fish populations were caught. This knowledge has implications for the effective rehabilitation of lowland river fish communities and the improvement of the River Res. Applic. 28: 1189–1199 (2012) DOI: 10.1002/rra

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ecological status of rivers under the European Union, Water Framework Directive (2000/60/EEC), especially heavily modified water bodies where much of the functional landscape has been lost through river engineering works and flow regulation. Furthermore, although the richness of fish is highest at maximum levels of connectivity, many non‐fish taxa attain peak species richness at different locations along the lateral connectivity gradient, and overall biological diversity is highest at intermediate levels of floodplain connectivity (Tockner et al., 1998); thus, the restoration of variable connectivity should not focus on single species or taxonomic groups (Sparks, 1995; Tockner et al., 2000). This study, therefore, supports the incorporation of artificial floodplain waterbodies of variable, not just high, levels of hydrological connectivity into holistic riverine ecosystem management plans. ACKNOWLEDGEMENTS

The authors would like to thank Jonathan Harvey, Richard Noble, Darren Rollins, Ryan Taylor, David Hunter and Laura Wigley for their assistance in data collection. Support was provided by the Environment Agency under Science Project SC030215 ‘Dispersal Behaviour of Coarse Fish’. We are grateful to Graeme Peirson for his assistance with project support and to all landowners for permission to access the river.

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