Agriculture and Stream Water Quality: a Biological ...

Agriculture and Stream Water Quality: a Biological Evaluation of Erosion Control Practices DAVID R. LENAT

Narth Carolina Department 01 Natural Resources and Communily Development Water Qualily Section, Arc hdale Building PO Box 27687 ;:.~!e i gh, North Carolina 276 i 1USA kSSiRACT I Aoricultural runoii affects me ,. y sireems in North Caro ILIG. However, th~~S is lir::e iniorm2 tion 2bcut e'ther its effect on s:-e2m biota or an~otenti21 mitig2tion by e~osion contro l practices. 1;'1 this study, benthic mecroinvertebra ies were sampled in three dil f;;rent geographic areas 01 North Ccrolina, comparing control wa t;;rsheds with well-manages and poorly menc·;;ed watersheds. Agri

.,

Agriculture is the largest industry in Nonh Carolina with farm production exceeding S3 billion per ye2.r. Cropland and pG.Sture comprise 26'70 of tne state's land area. Runoff from this area may contain a variety of non point pollutants such as s..."'oil and water conservation practices benefit both land and \';ater systems could be used as a rationale for a greater emphasis on erosion control. Many recent studies of agricultural runoff have focused on nutrient delivery (Omernik J977). In North Carolina, algal bloom problems in coastal areas have intensified the need for such nutrient inl'estigations. This type of study, however, tends K.::""Y WORDS : Agricullure ;

6enl~'c

r;;acroinveriebrales: Erosion conlrol ; Sedi

ment; Waler quality ~;;vironmenlal

l..tanagemenl. Vol. 8. No.4, pp . 333-344

cU:lural streams were characterized by lower laxa ric~_-.lem. T,e effects of agricultural runoff on s'ream fau;-,2, ha ve rz..-e!y c.c~n detennined. Consequently, the effectil'cess of "bes t r.:anagement practices" (BMPs) in pre'.'e:lting s:;~am deg~dc. tion is also poorly known. . Marsh and Waters (1980) found that agricul:ural dra::1age n2.d little effect on the invenebrate fauna 0; "undistl!rbed downstream reaches." Dance (1978) compared ,',,'0 branches of ::':1 Ontario stream, one forested and one affec:d by ag;icul L,al drainage. The ag;-icultural branch hac! a h i ~her sedi",e:ll lead, higher summer temperature and higher ir,;~;mitleni flow ;~,3.n the forested branch, These physical-che:;::CG I diffeiences I, ere associated with a difference in the ben;h:c (ommu01ities. l?xa richness for intolerant groups (Plecopte;c. Ephemerop iera, Trichoptera) declined while taxa richr,~,s for cenain :~!erant groups (Coleoptera, Odonata) increas~. McCafferty ( i 9(8) also has associated a decline in the lc.xa richness of Ephemeroptera, Plecoptera and Trichoptera I\'i,n agricultl!ral r2noff. Welch and others (1977) conducted a SUf\'e:' of 33 streams i;-, New Brunswick; 12 of these streams were 10C2:ed i n ar~as of i;:lensil'e potato farming. Agricultural drainage increased both ,diment load and stream conductivity. Some evidence also "2ggested pesticide contamination in nlany stre::..:ns. The "bun (2nCe of both fish and macroinl'ertebrates was lower in c~ricultural streams than in control streams. A si1ift in commu ;:ity structure was found at the agricultural sites, with tolerant Diptera replacing intolerant Ephemnoptera c.~ P-leC?ptera, Such a shift suggests a decline in water quality. Similar results I,ere obtained by Bratton and others (1980). T'ley also found ,hat differences between control sites and agricultural sites ",'ere less evident after a management plan ""2, instituted to reduce the impact of agricultural drainage.

© 1984 SpringeJ,V:e stecy sites include a wide variety of geographic regions. Tr:~ee st,ams were selected in each study area: a control site (stai ion 1), a well-managed site (station 2) and a poorly managed site (s;;otion 3). The control site was chosen from a group of streams pr~\'iously sampled (physical-chemical) by the US Geolog ical SI.!,\'ey (Simmons and Heath 1979) in an attempt to define ur,;olluted, baseline water quality in Nonh Carolina. L"d u~ in these watersheds was primarily forest with some inaC'i l'e ag~cultural land. The well-managed and poorly managed watersheds were se : ~([ed by the local Soil Conservation Service District Conser v;o:ionist. The District Conservationist was asked to use ihe fo!!owing criteria: I) Select areas roughly equivalent in size to the control. 2) Omit any areas with point source discharges, ani;;Jal waste problems, etc. 3) Emphasize currently recommended management prac tices in selecting well-managed areas.

I .)

2i

12l. y. .

Buffalo Shoals

Olin Cr.

StL.:dy Areas

5,301

5.4

3.0

4)

C~.

Bells

3,274

4,824

~

72

Little

C~.

I ,6~2 11.5 2: 1~

56

Aver;' C.-. 7,00':' b .:

14 14

2'=1

57

65

10

If detailed erosion rates are lacking, ai:e:;-tpt to select watershed such that erosion of the (C·:mol site < well-managed site < poorly managed sice. Follow-up quesiionnaires were sent to the Dis:~ct Conserva tionist to verify these trends . Detailed informatio~, wa~ solicited on watershed size, crops, no. animals/ acre, calc-,,:aied sad loss, soil type and erosion control practices. The inten: was to obtain all available information with no expectation thz: all questions could be answered. Results from the questionnaire (Table 1) confirmed the initial selection of watersheds. Erosion rates \,~re estimated using the "soil loss prediction eo, uation." Soil loss increased from the control sites to the well-managed sites w the poorly managed sites. This gradie:lt of impact is the rr:ost imponant element in the study design. The practice most often cited by the S.C.S. representatives for the poorly managed watersheds was "straigh: row" (up and down slope) cultivation. Many erosion control te(hAiques were employed on well-managed watersheds. The most commonly employed practices were "conservation tillage," ir.c1uding min imal tillage, use of crop residue and contour iillage. Other commonly used BMPs included crop rotation, mip cropping, cover crops, terracing and use of field border.

~

Agriculture and Stream Water Quality

No watersheds were known to have problems associatecl with fertilizers, pesticides or 2nimal wastes. Most watershees contained 100-200 cattle or hogs. Streams were sampled three times: Januart , May-June and .-\ugust. One station was sampled in each stream. T,te original intention was to sample during (a) a pe:iod of low agricultural activity (winter), (b) a periO;


Table 6.

Table 7. Temporal st2bility of community struc!ure: mean standard deviation (n - 7-8) of within-group % dominance.

Leve!-II data, Buncombe County, 1981. Month:

May

Station:'

2

Rounded average

August 3

2

2

3

Station 3

II

8 9 3 6 I:'

1 3 56

14 6 8 4

7 13 4

,

"T

60

8 8 12 II 8 12 13 4 1 6 3 2 3 8 5 6 6 7 4 8 6 3 2 3 7 4 3 5 5 4 3 5 5 5 9 12 15 4 4 8 10 , 3 2 1 3 1 I , 4 ·3 2 2 3 3 43 36 38 36 46 49 40

B) Dennty (%)

Ephemeroptera Pkcoptera Trichoptera Coleoptera Diptera Other

Control

Well managed

Poorly managed

Richmond County Iredell County Buncombe County

5.2 4.9 4.2

5.5 7.9 8.4

7.7 14.5 16.1

Mean

4.8

7.3Q. .

Study area

:\) Taxa richness

Ephemeroptera Plecoptera Tricoptera Coleoptera Diptera: Misc. Diptera: Chiron. Oligochaeta Other Total

47 17 19

5 11

69 86 34 32 13 1 1 8 1 21 3 44 5~ 81 , 1 1 2 7 2 .i 8 11 2 1 6

41 13 32 3 11

339

51 50 1 1 38
ture was re latively s;,;.ble at control sites, but the treated streams had marked reductions in the abundance of Plecoptera, . Ephemeroptera and T;ichoptera. Such organophosphate pesti cides degrade quickly in the environment relative to organo chlorides, but have a very high toxicity (Holden 1972). The similarity of our resul:s to those of Counemanch and Gibbs (1980) suggest that \"~\er quality of agricultural runoff, in addition to sediment impacts, may anect stream biota. How ever, these results should be cautiously interpreted as the groups Plecoptera, Epn~meroptera and Trichoptera are sensi tive to many kinds of sere,s. Disln'bulion of taxa C;";long slalions. Further analysis was conducted using a singie data set where all dates had been combined (Table 8). Only two groups were examined here: "tolerant" and "intolerc.nt" taxa. Intolerant taxa were defined (from prior analysis) as the sum of Ephemeroptera, Plecoptera, T richoptera and Odonata. General trends in total species richness were similar to those seen for al'erage taxa richness (Table 2). The intolerant tax? declined at all three poorly managed sites, but declined at only one well-managed site. Tolerant taxa showed a large decline only at one agricultural site (Richmond County, station 3) and an increase was seen at the Buncombe County sites. The decline for tolerant species at the poorly managed Richmond County site was largely due to a reduction in the number of Chironomidae. This is a very large group, encompassing many species with varying degrees of tolerance. Examining the dis;ribution of species among stations also can yield data on the dims of agricultural runoff. If agricul-

Table 9. Reduction in taxa richness values (%). relative to .control values.a

Station:

Average of monthly vatues b

All months com~ineci(

Well managed

Poorlv managed

Well manageci

22

23 31

23

15 38 6

37

15 59 .!2

Poorly m2.~2geci

A) Total

Richmond Co. Iredell Co. Buncomlx Co.

13

B) Intolerant

Richmond Co. Ireddl Co. Buncombe Co.

30 8

'Dash inciiCltc:s zera or a POSilive value. bSe~ Table 2. 'Sec Table 7.

32 50 42

'"

ture does not affect water quality, there should be an equal number of unique species at each station. A "uniql.!e" species is defined here as occurring at only one of the three stations in each study area. It does not i~ply any other ch2.rc.cteris,ics for that species. A similar analysis was used to assess copper toxicit y by Winner and others (1980). In all three study areas (Table 8), there were more species limited to s:ation 1 (the control) than are limited to station 2 or 3. This dinerence averages out to a decline of about 38"10: a grand mean of 32 taxa at station 1 versus 19-21 taxa at stations 2 and 3. This difference is statistically significant (paired-I, P < 0.05). We might expect good erosion control to yield more unique species at station 2 than at station 3, but this patte:-n was observed only in Iredell County. This pattern implies that some effects of agricultural runoffs are unavoidable and 2.re not reduced by good erosion control. Lenat and others (1983) have discussed the enects of sedimentation on the macroinvertebrate community. They predict that increasing sample sizes (for example, by pooling samples) will decrease differences in taxa richness between control and sediment-impacted sites. Sample size was increased in this study by combining the monthly informalion into a single data set. Table 9 compares the reduction in taxa richness values (versus the control) for this larger data set with the reductions observed using average monthly values. These results implicate sediment as the major problem.at .Rir~mond County and Buncombe County sites ..\t IredelC County sites, however, the reduction in taxa richness is more evident for the larger data set, especially for the intOlerant groups. These results suggest that water quality changes also may have affected the stream biota.


Table 10.

341

Taxa unaffected, or favored , by ;:;ricultural runoff. Tot2.!

Taxon

~umixr eoll~et~d

F~~ding t)yc'

2

3

55 228

321 240 876 2,911 241 149

1,443 155 330 1,446 259 242

96 50

181 368

250 446

1,0iO

35

3,398 li6

3,656 442

365 4 101

352 5 14

274 161 398

Scrapers, colkctors-gathe~ers

Scrapers, collectors-gathe~ers .

Scrapers

33 129

186 158 li6

94 84 111

Collectors- fil ter~rs Coll~ctors- fil ter~ rs

Station:

Eph~m~ropl~ra

Baetis amp/us B. in/erca/aris Pseudocloeon sp. E,bhemerella catawba E. dejiciens fsonychia spp.

33 56 213 7' . ."

PI~copt~ra

Taeniop/nyx sp. Brachyp/era sp.

T riehopt~ra Cheuma/opryche spp. Hydropryche bel/em'

Coil~etors-gath~r~rs, ·SGc.~rs

Coll~etors-gath~r~rs,

Scr2pers

SCTapers

Colleetors-gath~rers , seRpers

Co!l~ctors-gatherers, SCTa!Xrs

Coll~~q;:.-filterers .

Coll~ctors-gath~rers,

~

Shr~dders-d~tritivores, coiketorS-~therers,

scrape::

Scrapers

Collectors- fil t~rers

Colkc:ors- fi lterers

Cokopt~ra

Oulim:1ius /a/iuscu/us Stene!mis spp. Psephenus herricki Diptera An/ocha sp. Mirro/endipes pedellus(?) Rheo/ar.ylarsus spp.

iSO

Collectors-gath~r~.--s, scr2~r

#

'Stt ttxt for definitions.

Dala rumman'zed at lhe species, or laxoT:, !cue! Due to the large size of this dat2. set (275 taxa), detailed discussion was not practical. Instead, emph~sis was placed on de:ermining which species were toler2.nt of ~g,icultural runoff. This information can be used to char2.c:erize the benthic community of streams in agricultural areas. Agricultural runoff can affect food s\,;pplies of benthic macroinvertebrates either by the addition of particulate organic matter (POM) or by the addition of nutrie:1[s which promote algal growth. This type of effect can be eX2.I71ined by looking at the feeding types of organisms found in agricultural streams. Table 10 lists species whose abundance was unaffected, or fa vored, by agricultural runoff in at least two of the three stud y areas. This list includes only those species for which greater than 150 indi viduals were collected. The response of any single species can be highly variable, sometimes increasing in one study area, but declining in another. Runon irom each agricul tural area can have unique characte:-istics, depending on soil type, crop, and the application of chemids. Feeding types (from Merritt and Cummins 1978) are as follows: Shredders-Feed on decomposing vas(Ular plant tissue, coarse particulate organic matter (CPOM) CollectOrs-Feed on decomposing fine particulate organic matter (FPOM) Filterers -Suspension feeders Gatherers-Feed on deposit organics

Scrapers -Feed on attached 2.lgae and assoc!2.ted materi als Organisms charac.e,istic of agri0)tural streams fall into three major groups: scrapers, collector-gathere,s and filter-feeders . ~.fany organisms C2.n be conside,td as either collector-gather ers or scrapers. The increase in flter-feeders suggests that the concentration of susper.ded p",,-,icuiate organic matter is greater in agricultural streams l:.an in control areas. Deposi tion of this material leads to incr:~se in deposit feeders . Inputs of nutrients will stimulate peripi-,yton growth, which leads to an increase in scraping organism;. Many of these scrapers are associated with stable-sand substrates. Most of the Ephemeroptera (r.,ayAies) listed in Table 10 are scrapers. Baetis (two species) anc Pseudocloeon spp. were most important in the piedmont areas 2nd Eph em erella catawba was the most important mayfly in the mountain area . These mayflies were panicularly abund2.nt in the spring during a low flow period when stable· sand c-ommunities de'/e1oped. Only two Plecoptera, Brachyplera and Taeniopteryx, were resistant to'agricultural sites. Both of the Trichoptera resistant to agricultur?J nmoff were filter-feeders. These summer dominants were important at both piedmont and mountain sites. CheumatopsycJ.e spp. and Hydropsyche bellen i were especially abundant in summer samples from agricultural siLes (;tations 2 and 3). Coleoptera, especially certain Elmidae, were abundant at agricultural

842

"

D. R. Lenat

st,eams in piedmont and rTcJuntain areas. This was the only group whose abundance wa; unaffew:d by agricultural runoff. The response of Diptera I'(2S very erratic. Only two filter feeders and one grazer we,: consistently resistant to agricul tural runoff. Many chiro;;omid species were occasionally favored by agricultural runoff, but the pattern was not predict ab le. Some of the taxa favore:: by agricultural runoff also have been found 1.0 increase in z.::.as disturbed by logging. Several studies in Coweeta Natiorc.:.l Forest (North Carolina) have recorded increases in Bae!is ;pp., Psrodocloeon sp., Epherner ella spp., Taeniopteryx, h:!ocha and Chironomidae (Gurtz 1981, Haefner and WallaC! 1981). However, no increase was observed for filter-feeding ~-:Ges.

Conclusions Agricultural runoff can impact stream biota by changing either substrate compositio:-i, water quality or food supplies. Although agricultural rUDen is generally believed to affect water quality (Loehr 1979), little is known about the effect on stream communities. Even :~ is known about the mitigating eff~ct of erosion control puc-jces. Studies were set up in ,-~ree different geographic regions: mountain, piedmont and S2ld hills. Within each study area, benthic macroinvenebrateo were sampled in well-managed, poorly managed and contro! watersheds. Average taxa richness, a parameter directly related to stream quality, was always greater at well-managed sites than at poorly managed sites. h two out of three study areas, no difference in average ta~ richness was observed between control sites and poorly :::anaged sites. However, average· abundance could not be CJnsistentiy rc:lated to agricultural activity. An increase in the biotic index (indicating a shift to more "tolerant" species) ..... 2.5 observed only at the mountain area. Plecoptera, Ephemerop'era and Trichoptera were the groups most severely affec:~ by agricultural runoff, with the greatest decline in taxa ric.~~less occurring at poorly managed sites. Agricultural streaflli . especially poorly managed sites, were characte;-ized by la~~ temporal shifts in the taxonomic composition (percent abund"nce) of the benthic fauna. Stability (measured by a mean standard deviation) was significantly greater at cGltrol sites, especially relative to poorly managed sites. Certain impacts of agricultural runoff are not affected by erosion control. An exam~;]ation of the distribution of taxa among stations found that a lower number of unique taxa (that is, found at only one site) ccrurred at both well-managed and poorly managed sites.

The taxa favored by agricultural runoff included collector gatherers, scrap=s and filter-feeders. This suggests that agri cultural runoff E.H·eClS food supplies by stimulating periplyton and by u,.e addiLion of particulate organic matter. This study demonstrates that agricultural runoff can seve:-ely impact meam communities. Howeve:-, good erosion control greatly sitigates this impact.

,A,ckowledgms;lts This paper ".!mmarizes a report prepared for the North Carolina Divis;o;] of Environmental Management (Biological Series no 107). Staff 'members of the Biological Monitoring Group who aid~ in sample collection, sample processing and computer analy;-."'S included David Penrose, Kenneth Eagle son, Kay DecI-:.:J1t, Dana Folley, Ferne Winborne, Mike Birckhead, Ros.; Green and Larry Ausley. The patience and support of my ·...·ife, Georgia Hage:1, is gratefully acknowl edged. Walter High (Richmond Co.), J01m Caviness (Iredell Co.) and Jesse OWe:.5 (Buncombe Co.), local Soil Conservation Personnel, coop--:-atetl in the site selection process and supplied land use inforrn.2.:ion. Detc.iled cor._-nents on a draft manuscript were supplied by Beverly You ny, Buddy Atkins (N.C. State University, School of Agriculture E...ld Life Sciences) and William McClelland (N.C. Depanr.,!:1t of Agriculture). Useful criticism was also received from ?\!lson R. Nunnally, Don C. Erman and T. G. Danie l.

Literature Citsd Armitage, P. D. 1978. Downstream changes in the composition numbers and :;omass or bottom rauna in the Tees below Cow Gree;] ReservD~- and an unregulated tributary, Maize Beck, in the first five years ~'ter impoundment. Hydrobiologia 58: 145-156. Bratton, S. 0., R. C. \fathews, J r., and P. S. White. 1980. Agricul tural area im:2CtS within a natural area: C2des Cove, a case histOrf. Enuir~. Manage. 4:433-448. Cook, K. 1982. S:illos.s: a question or values. j. Soil Water Conserv. 89-92.

Counemanch, D. 1., and K. E. Gibbs. 1980. Short and long-term effects or ror~~ spraying or Carbaryl (Seyen-4 oil) on stre2.IT1 invertebrates. C1n Enlornol. 112:271-276. Dance, K. W. 1;78. \facroinvertebrate diversity in two streams as affected by agf.cultural land use. Presented at the annual meeting or the North .!_';"lericzn Benthological Society, Winnipeg, ~1anitoba, May 1978. Division or Envi;:,nme.ntal Management. 1979. 208 1 results. Division or Envi~nmental Management. 1983. Qualitative sampling or benthic mac:-oim'ertebrates: a reliable cost-effective biomonitor ing technique. Biological Series no. 108, 11 pp.