Geo-Marine Letters https://doi.org/10.1007/s00367-018-0549-3
ORIGINAL
Tidally driven sulfidic conditions in Peruvian mangrove sediments Alexander Pérez 1,2 & Dimitri Gutiérrez 1,3 & Maritza S. Saldarriaga 4 & Christian J. Sanders 5 Received: 24 July 2018 / Accepted: 28 August 2018 # Springer-Verlag GmbH Germany, part of Springer Nature 2018
Abstract The seasonal influence of tidal regimes on sulfidic conditions was studied in intertidal environments from a mangrove estuary in Northern Peru. Along two sampling stations, creek water and sediment cores were collected during the dry and wet seasons at all tidal phases (ebb, low, flow, and high tides). Physical-chemical parameters were measured in the creek water (temperature, salinity, pH, Eh, and DO), whereas pH, redox potential (Eh), and total organic matter contents were obtained from the sediment cores. In addition, total dissolved sulfide content ∑ (H2S, HS−, H2−) was measured from sediment pore water. During the dry and wet seasons, the creek water pH, Eh, and dissolved oxygen were lowest in low tide, whereas oxygenated conditions and higher pH and Eh values prevailed in high tide. The total organic matter content in sediments was higher during the dry season, with the highest contents observed in the seaward station. Higher average ∑H2S (landward station, 243.1 ± 234.9 μM L−1; seaward station, 544.9 ± 174.4 μM L−1) were noted during wet season compared to dry season (landward station, 5.3 ± 4.5 μM L−1; seaward station, 430.2 ± 435.1 μM L−1). These ∑H2S contents increased towards the bottom of the sediment column, reflecting the anaerobic decomposition of the organic matter and sulfate reduction. This study provides insight to the geochemical dynamics of intertidal mangrove sediments that are sensitive to fluctuating reducing and sulfidic conditions, oscillating at time scales of minutes to hours.
Introduction Mangrove forests are highly productive ecosystems that play an important role in the atmospheric, terrestrial, and marine
* Alexander Pérez
[email protected] * Dimitri Gutiérrez
[email protected] 1
Centro de Investigación para el Desarrollo Integral y Sostenible (CIDIS), Facultad de Ciencias y Filosofía, Laboratorios de investigación y desarrollo (LID), Universidad Peruana Cayetano Heredia, Av. Honorio Delgado 430, Urb. Ingeniería, Lima 31, Peru
2
Instituto Geofísico del Perú, Área de Investigación en Prevención de Desastres Naturales (Clima), Calle Badajoz 169 Mayorazgo IV Etapa - Ate Vitarte, Lima, Peru
3
Instituto del Mar del Perú, Dirección General de Investigaciones en Oceanografía y Cambio Climático (DGIOCC), Av. Gamarra y General Valle, s/n, Chucuito, Callao, Peru
4
Instituto del Mar del Perú, Dirección General de investigaciones de Recursos Demersales y Litorales (DGIRDL), Av. Gamarra y General Valle, s/n, Chucuito, Callao, Peru
5
National Marine Science Centre, School of Environment, Science and Engineering, Southern Cross University, Coffs Harbour, New South Wales, Australia
carbon cycle, as these systems sequester and bury ~ 20% of the coastal sedimentary carbon (Kristensen et al. 2008; Alongi 2014; Sanders et al. 2016a). However, the organic matter accumulation rates within these ecosystems may be influenced by natural factors such as the forest geomorphology, seasonal hydrological regime, and tidal phases (Sanders et al. 2016b; Chmura et al. 2003; Pérez et al. 2017). Recent studies have indicated that tidal regimes may influence the short-term physical-chemical and geochemical properties of creek waters and sediments, modifying the organic matter decomposition rates and carbon cycle within these systems (Bouillon et al. 2008; Breithaupt et al. 2014; Alongi 2014). The northernmost Peruvian semi-arid mangrove ecosystem is exposed to seasonal rainfall, freshwater input from the Zarumilla River and semidiurnal tidal regimes (INRENA 2011; Pérez et al. 2017), which may affect particle transport and thus the accumulation, decomposition, and mineralization of organic matter within the sedimentary environments (Kristensen et al. 2008; Alongi 2009, 2014). This study aims to determine the effect of seasonal tidal phases on the physical-chemical conditions in creek water as well as on the development of sulfidic conditions in intertidal sediments within this Peruvian mangrove estuary. We hypothesize that the tidal regime is a main factor that modulates the buildup of sulfidic conditions in the intertidal sediments of this mangrove system. The hypothesis is tested by measuring specific geochemical parameters, including pH, Eh,
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Sanctuary BManglares de Tumbes^ (~ 30 km2) (INRENA 2011). This study area is characterized by a semi-arid climate with temperatures ranging from 22 to 32°C, which is influenced by the Zarumilla River and its secondary creeks (Spalding et al. 2010; Pérez et al. 2017). The mangrove sediments in this region are high in silt and clay and are characterized by a ~ 1–5% slope topography from the Pacific Ocean to the continent (INRENA 2011). The creeks ranged between 1.0 and 3.5 m in depth (during high tide) and present a semidiurnal tidal regime with maximal amplitudes of ~ 2 m during spring tides and ~ 1 m during neap tide (INRENA 2011; Pérez 2014). This area contains distinctive wet and dry seasons; the dry season (June to December) is characterized by the lack of rainfall and a decrease in the Zarumilla River water flow (0.03 to 1.48 m3 s−1), and the wet season (January to May) is characterized by higher average
and dissolved sulfide content during seasonal and tidal phases. Given that sulfate reduction is the main anaerobic pathway in organic matter decomposition within mangrove sediments (Black and Shimmield 2003; Alongi 2009), the results of this study will contribute in shedding light on the influences of the tidal regime on the geochemical dynamics related to organic matter decomposition in these sediments.
Material and methods Study area The mangrove ecosystem studied in this research is located in the Northern coast of Peru (Fig. 1a) and is associated to the National
a
ECUADOR
LC
PERU
AC
b Sampling station High tide Low tide Fig. 1 a Map of the study area within the Mangrove Sanctuary. b Sampling station within the mangrove estuary (red bar). AC, Algarrobo creek; LC, Lagarto creek
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temperatures, heavy rainfalls (400 to 1000 mm), and the increase in the Zarumilla River water flow (5 to 43 m3 s−1) (INRENA 2011; Morera 2014; Pérez et al. 2017).
Sampling design The sampling campaigns were undertaken in the dry season (November 22–23, 2012) and in the wet season (April 6 and 7, 2013). The fieldwork was carried out under daylight and in the same sampling stations for both campaigns (Fig. 1b). During each campaign, two sampling stations were studied at all tidal phases (ebb tide, low tide, flow tide, and high tide): Algarrobo Creek (AC), near the freshwater source to the estuary, and Lagarto Creek (LC), located towards the middle of the estuary (Fig. 1a). The physical-chemical parameters in the creek waters were measured in duplicates (temperature, salinity, pH, Eh, and DO) using water quality testing equipment (Horiba U-51). During the sampling campaigns, 10-cm-deep sediment cores were collected using a hand-core sediment sampler (Model 77258, WILDCO, Florida, USA) (Fig. 2a). At all tidal phases, two sediment cores were collected to determine the redox potential (Eh) and pH measurements at 2-cm-deep resolution using a redox-pH sensor for sediments (WTW–1081). During low and high tides, two sediment cores were extruded and sectioned at 1-cm-deep resolutions (Fig. 2b) for analyses
a
Sediment
Results and discussions Changes in creek water and intertidal sediments During the dry season, the creek water temperatures were lower (from 25.5 to 26.5 °C) as compared with those registered during
c
1 cm
10 cm-depth
Creek-water
b
of total organic matter content (TOM). The TOM was determined by the difference between the weights before and after combusting at 550 °C, following the methods described in Black (1965). Furthermore, at all tidal phases, two sediment cores were collected for ∑(H2S, HS−, H2−) or ∑H2S measurements in pore water at 1-cm-deep resolution using Rhyzon® capillary samplers connected to syringes (Fig. 2c–d). Then 2 mL of pore water was extracted and preserved in vials with 0.5 mL of 5% zinc acetate and frozen until analyses. In laboratory, ∑H2S content was measured by spectrophotometry following the method of Cline (1969). The tidal amplitude for both sampling stations (Fig. 3) was obtained using a data logger (Solinst Levelogger Edge 3001, Canada). Finally, the spatial variation of each parameter at all tidal phases were evaluated through a two-way analysis of variance (ANOVA) (α = 0.05), followed by the post hoc Tukey’s Honestly Significant Difference test (ANOVA + Tukey HSD).
3 cm 2 cm 7 cm
6 cm
5 cm 9 cm
4 – 8 cm
10 cm
1 - 5 – 9 cm
2 - 6 -10 cm
3 - 7 cm
Extruder
d
Fig. 2 Conceptual diagrams of a sediment core sampling (a), extrusion and sectioning design of the sediment column (b), and pore water sampling using Rhyzon® spirally arranged (c, d)
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Algarrobo Creek
Fig. 3 Tidal amplitude within each sampling stations. Red arrows point the day in which the samples were taken. (A) Dry season. (B) Wet season
Oct. 12 Nov. 12
Jan. 13 Feb. 13 Mar. 13 Apr. 13 May. 13 Jun. 13
Dec. 12
Tidal amplitude (m)
Sep. 12
b
Tidal amplitude (m)
a
Days
Days
Lagarto Creek Jan. Feb. Mar. 13 Apr. 13 May. 13 Jun. 13
Tidal amplitude (m)
Aug. 12 Sep. 12 Oct. 12 Nov. 12 Dec. 12
b
Tidal amplitude (m)
a
Days
Days
Table 1 Physical-chemical conditions in creek water during each tidal phase for the dry and wet seasons. AC, Algarrobo creek; LC, Lagarto creek; Depth, water column depth; DO, dissolved oxygen content Tidal phases
AC—low tide AC—flow tide AC—high tide AC—ebb tide LC—low tide LC—flow tide LC—high tide LC—ebb tide
Dry season
Wet season
Depth (m)
T (°C)
Salinity
pH
Depth (m)
T (°C)
0.50 – 2.30 – 0.70 – 2.30 –
25.6 ± 0.3 – 26.5 ± 0.5 – 25.5 ± 0.4 – 26.5 ± 0.3 –
35.1 ± 0.8 – 34.1 ± 0.2 – 35.8 ± 0.5 – 33.5 ± 0.3 –
7.4 ± 0.3 – 7.6 ± 0.1 – 7.3 ± 0.4 – 7.9 ± 0.2 –
0.30 0.90 2.00 1.20 0.30 1.30 2.50 0.60
29.4 30.6 30.3 30.1 28.9 29.5 28.2 28.5
± ± ± ± ± ± ± ±
1.1 0.7 0.5 0.8 0.3 0.4 0.5 0.3
Salinity
pH
27.2 21.5 22.9 23.2 27.1 24.3 27.8 27.0
7.0 7.2 7.9 7.6 7.4 7.8 8.0 7.9
± ± ± ± ± ± ± ±
0.3 1.2 0.7 0.3 0.4 0.5 0.4 0.7
± ± ± ± ± ± ± ±
0.1 0.3 0.2 0.2 02 0.3 0.3 0.1
Eh (mV)
DO (mL L−1)
− 236.2 ± 14.2 − 37.4 ± 1.3 1.5 ± 2.5 12.1 ± 3.1 − 41.1 ± 2.2 − 40.5 ± 1.0 − 22.5 ± 1.5 − 33.8 ± 2.1
0.04 ± 0.01 4.5 ± 0.4 5.0 ± 0.03 4.0 ± 0.7 1.81 ± 0.1 3.9 ± 0.2 4.3 ± 0.3 1.8 ± 0.4
Geo-Mar Lett Table 2 Two-way ANOVA results for seasonal and spatial dynamics during the tidal regime. D, dry season; W, wet season; AC, Algarrobo creek; LC, Lagarto creek; n.s., statistically not significant; *p < 0.05. Underlined acronyms represent factors with non-statistical differences among them
pH[Superficial sediment] Eh[Superficial sediment]
Season
Sampling station
Season vs. sampling station
*(D < W)
n.s.
*
n.s.
*
*(AC < LC)
*
n.s.
ΣH2S[Pore water]
n.s.
TOM[Superficial sediments] ΣH2S[Pore water]
the wet season (from 28.2 to 30.5 °C) (Table 1). During both seasons, higher salinities (up to 35.8 in the dry season) were recorded during the low tide at all sampling stations (Table 1). These high salinities may be related to the high evaporation rates during daylight insolation, which may be amplified in shallow water columns and intertidal sediments (Borges et al. 2003; Kristensen et al. 2008). Furthermore, lower pH and Eh values in the creek water were observed during low tide (Table 1), reflecting likely higher CO2 release as a result of greater organic matter content along the superficial sediments (Fig. 6) (Black
pH
pH 6
7
8
9
a
2
Depth (cm)
Depth (cm)
b
2
9
4 6
10
10
Eh (mV) -320 -220
LagartoCreek
−−−−−−−−−−−−−−−−−−
0
2
2
4 6
b -420
Eh (mV) -320 -220
-120
4 6
8
8
10
10
High tide
-120
LagartoCreek
0
Depth (cm)
Depth (cm)
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6 8
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ðACW < LCW ACD LCD Þ
4
8
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−−−−−−−−−−−
*
Algarrobo Creek
0
8
ðACD < ACW < LCD LCW Þ
and Shimmield 2003; Borges et al. 2003; Sanders et al. 2015). The dissolved oxygen (DO) values were greater during high tide conducive with the incoming tide bringing oxygenated water into the estuary (Table 1). In addition, during the wet season, the Eh values were lower at all tidal phases in LC station as compared with those in AC (Table 1). These values suggest higher decomposition rates within LC, likely triggered by the higher sedimentary organic matter contents in comparison with AC station (Fig. 6) which associated to the estuarine hydrological dynamics may result in more reducing conditions in creek
-420 0
7
−−−−−−−−−−−−−−−−−
−−−−−−−−−−−−−−−−−−−−−
Algarrobo Creek 6
ðACD < LCW LCD ACW Þ
ðACHigh AC Flow < ACEbb LC Flow ACLow < LCLow LCHigh LCEbb Þ −−−−−−−−−−−−−−−
a
−−−−−−−−−−−−
*(W < D) *(AC < LC) Sampling station vs. tidal phase *
ðLCD < ACD ACW LCW Þ
Ebb tide
Fig. 4 Seasonal pH profiles in sediment column within Algarrobo and Lagarto creeks at all tidal phases. (A) Dry season. (B) Wet season
Low tide
Flow tide
High tide
Ebb tide
Fig. 5 Seasonal redox profiles in sediment within Algarrobo and Lagarto creeks at all tidal phases. (A) Dry season. (B) Wet season
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water (Black and Shimmield 2003; Pérez et al. 2017). The DO concentrations were lower during the low tide within both sampling stations (only wet season values are available due to problems with the equipment during the dry season) (Table 1), which may suggest a higher dissolved oxygen demand during the decomposition of organic matter in intertidal sediments and more oxygen diffusion in shallow creek waters during this phase (Bianchi 2007; Kristensen et al. 2008). The pH profiles in intertidal sediments exhibited the lowest values during the dry season within both sampling stations (Table 2). However, the AC station presented the lowest pH values in surface sediments during ebb and low tides (dry season: from 7.2 to 6.7; wet season: from 7.5 to 7.2), whereas the LC station exhibited the lowest pH values in surface sediments during the flow and high tides (dry season: from 6.5 to 6.3; wet season: from 7.6 to 7.2) (Fig. 4). Furthermore, the Eh profiles along intertidal sediments exhibited reducing conditions from the sediment surface towards the bottom of the sediment column (Fig. 5), with on average less reducing conditions, during the wet season. The AC station presented the most reducing conditions in surface sediments during low and flow tides (dry season: from − 340 to − 400; wet season: from − 160 to − 230), whereas the LC station exhibited the most reducing conditions during the high and ebb tides (dry season: from − 240 to − 300) and during the high and flow tides (wet season: from − 220 to − 300) (Fig. 5). Also, the lower pH and Eh values in superficial sediments of AC station (Figs. 4 and 5) were observed during the low tide in comparison with those during high tide which may be associated to the aerobic decomposition of the organic matter in exposed sediments during low tide (Kristensen et al. 2008; Pérez 2014). During this phase, higher oxygen consumption and higher CO2 production is expected (Borges et al. 2003; Black
and Shimmield 2003; Sanders et al. 2015), which would enhance the microbial degradation of the organic matter within this tropical mangrove (Fossing and Jorgensen 1989; Bouillon and Boschker 2006). In contrast, the lower pH and Eh values in superficial sediments of LC station (Figs. 4 and 5) were observed during high tide in comparison with those during low tide, which suggests that due to the higher organic matter contents in LC (Fig. 6), high organic matter decomposition rates may allow the re-establishment of reducing conditions in sediments. Therefore, the results here show that the reducing conditions in surface sediments are directly related to each tidal phase (Table 2). Note that the flow and ebb tides are considered as transition phases since they are influenced by geochemical processes occurring in the water and sediment columns during low to high tide transitions, which would rapidly modify the redox and pH gradient (Black and Shimmield 2003; Kristensen et al. 2008; Alongi 2009). Many studies have shown that sedimentary organic matter in mangrove systems is decomposed during aerobic and anaerobic bacterial respiration (Lymo et al. 2002b; Kristensen et al. 2008). During anaerobic decomposition of the organic matter, sulfate is used as the main electron acceptor, triggering sulfate reduction and consequent ∑H2S production that may occur at time scales form minutes to hours (Lymo et al. 2002a; Mendoza 2007). Thus, high ∑H2S content in pore water follows the higher decomposition rates of fresh and more labile organic matter, leading to rapid oxygen consumption and sulfidic conditions, which is driven by bacterial activity and enhanced in higher temperatures (McKee et al. 1988; Bouillon and Boschker 2006). These processes are also consistent with the higher ∑H2S contents observed during wet season (Fig. 7(B)), in which warmer temperatures and the greatest quantities of
Algarrobo Creek
Depth (cm)
a
TOM (mg 0 0
g-1)
60
TOM (mg g-1) 120 0
60
120
b
TOM (mg g-1) 0
TOM (mg g-1) 120 0
60
60
120
2
2
44 6
6
88
Low tide
High tide
Low tide
High tide
Lagarto Creek Depth (cm)
0 2
4 6 8
Low tide
High tide
Low tide
High tide
Fig. 6 Seasonal total organic matter (TOM) content at the Algarrobo and Lagarto creek stations at low and high tides. (A) Dry season. (B) Wet season
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labile organic matter prevailed in sediments (Pérez et al. 2017). In contrast, the lowest ∑H2S content was observed in the dry season and during low tide (Fig. 7(A)), suggesting the higher release of ∑H2S to the atmosphere, when the sediments are exposed and the freshwater intrusion is weak (Kristensen et al. 1994; Mendoza 2007; Pérez et al. 2017). Finally, during the wet season, the lowest ∑H2S content was noted in the high tide (Fig. 7(B)) indicating a flushing of the ∑H2S by the seawater and greater freshwater flux (Ovalle et al. 1990; Mendoza 2007; Pérez et al. 2017). However, the high ∑H2S content in the low tide during the wet season (Fig. 7(B)) would reflect the remnant influence of the neap tide, which limits the exposure
of intertidal sediments for a long period of time (Nickerson and Thibodeau 1985; Kristensen et al. 1994).
Geochemical dynamics within intertidal sediments In the seasonal dry conditions at the AC station (Fig. 8), during low tide when the sediments are exposed to air oxygen, the lower pH values in superficial sediments (Fig. 4(A)) are likely driven by the intense aerobic decomposition of sedimentary organic matter with limited ∑H2S production (Fig. 7(A)) (Bianchi 2007; Mendoza 2007). During flow tide and high tide, the incoming water brings higher concentrations of dissolved oxygen,
Algarrobo Creek
Depth (cm)
a
Sulfide ( M.L-1) 0 400 800 0 Low tide - 7:00hrs 2
400
800
1200 0
Flow tide - 10:00hrs
Sulfide ( M.L-1)
Sulfide ( M.L-1)
Sulfide ( M.L-1) 1200 0
400
800
High tide - 13:00hrs
1200 0
400
800
Ebb tide - 16:00hrs
4
6 8
10
Lagarto Creek Depth (cm)
0
2
Low tide - 7:00hrs
Flow tide - 10:00hrs
High tide - 13:00hrs
Ebb tide - 16:00hrs
4 6 8
10
Depth (cm)
b
Algarrobo Creek 0 Low tide - 7:00hrs 2
Flow tide - 10:00hrs
High tide - 13:00hrs
Ebb tide - 17:00 hrs
4 6 8
10
Depth (cm)
Lagarto Creek 0 Ebb tide - 6:00hrs 2
Low tide - 9:00hrs
Flow tide - 12:00hrs
High tide - 15:00hrs
4
6 8
10
Fig. 7 Seasonal ∑H2Sin pore water at the Algarrobo and Lagarto creek stations at all tidal phases. (A) Dry season. (B) Wet season
1200
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Bianchi 2007) resulting in a lower pH (Fig. 4(B)). In addition, the neap tide condition in this study may have limited the exposure of sediments to the air oxygen, limiting the aerobic organic matter decomposition and favoring the establishment of sulfidic conditions in pore water (Fig. 7(B)). The flow tide supplies the creek water with dissolved oxygen (Table 1), decreasing the reducing conditions in sediments (Figs. 4(B) and 5(B)) and limiting the ∑H2S production in pore water (Fig. 7(B)). Successively, during ebb tide, the creek water contains lower dissolved oxygen (Table 1) due to the higher organic matter decomposition (Bianchi 2007; Mendoza 2007) coinciding with higher ∑H2S pore-water concentrations (Fig. 7B). In the same season, the LC station (Fig. 8) also exhibited less reducing conditions than in the dry season (Figs. 4 and 5) with higher organic matter contents (Fig. 6(B)) that are linked to the higher local temperatures (INRENA 2011; Pérez et al. 2017) which may result in dissolved and air oxygen consumption during the ebb and low tides respectively (Lymo et al. 2002b; Mendoza 2007), triggering sulfidic pore-water conditions (Fig. 7(B)). During the flow tide, the dissolved oxygen flushes the surface ∑H2S pore-water contents, though not enough to support the establishment of aerobic conditions, resulting in low pH and Eh values (Figs. 4(B) and 5(B)), possibly due to the oxidation of free sulfide released deeper in the sediment column (Fig. 7B). These results suggest that the tidal influence is evidenced by the changes in pH, Eh, and ∑H2S in pore waters reflecting the exchange between aerobic and anaerobic conditions within intertidal sediments. However, further studies are necessary in different settings in order to better understand the constraints of these geochemical processes during tidal fluctuations.
triggering higher pH and Eh values (Figs. 4(A) and 5(A)) and, consequently, limiting the ∑H2S production and accumulation in sediments (Fig. 7(A)). Finally, during ebb tide, the dissolved oxygen in creek water and the tidal amplitude seem to favor aerobic decomposition of the organic matter with consequently lower ∑H2S concentrations in the pore water (Fig. 7(A)). In the same seasonal conditions at the LC station (Fig. 8), the intrusion of air oxygen into the exposed sediments during low tide may hamper the ∑H2S accumulation in pore water (Fig. 7(A)) during organic matter decomposition (Ovalle et al. 1990; Black and Shimmield 2003). However, the pH values at the LC station remained lower than those at the AC station (Fig. 4). The flow and high tides bring high dissolved oxygen content to the creek water (Table 1), though probably insufficient to support the aerobic decomposition of the available organic matter, which is higher in this station (Fig. 6(A)). Also, the intense decomposition of the organic matter may have dropped the sediment pH and Eh values (Figs. 4(A) and 5(A)), allowing greater anaerobic conditions, which is evidenced by the sulfidic conditions of the pore water (Fig. 7(A)) (Kristensen et al. 1994; Mendoza 2007). In the wet season, there is a clear difference related to the effect of the changing temperatures and the tidal amplitude on the reducing conditions and sulfide production along the intertidal sediments of both sampling stations (Fig. 8). The AC station exhibited less reducing conditions in wet season as compared with that in the dry season (Figs. 4 and 5). This is likely a consequence of the seasonal hydrological regime within the estuary (Pérez et al. 2017). During the low tide, the exposed sediments and higher temperatures turn these sites into hotspots of organic matter decomposition (McKee 1993;
Fig. 8 Conceptual model of the geochemical dynamics in the intertidal sediments during the low and high tidal phase in the dry and wet seasons
Dry Season (Low de)
OM aerobic respiraon Lower pH
Lower Eh
Limited ∑H2S producon
Wet Season (Low de)
Higher dissolved O2 content in creek water Covered sediments OM aerobic respiraon Higher pH
Higher Eh
Limited ∑H2S producon
Dry and wet Season (High de) Not enough dissolved O2 in creek water
Higher temperature
Air O2 intrusion
Limited sediment exposure Higher aerobic and anaerobic OM respiraon Lower pH]
Lower Eh
∑H2S producon
Lagarto Creek
Algarrobo and Lagarto Creek
Exposed sediments
Algarrobo Creek
Higher air O2 intrusion
Dry and wet Season (High de)
Covered sediments OM aerobic and anaerobic respiraon Lower pH
Lower Eh
High ∑H2S producon
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Conclusion This research provides evidence that tidal regimes are driving factors on the geochemical processes in mangrove ecosystems, modulating the reducing and sulfidic conditions in creek water and intertidal sediments on temporal and spatial scales. The results here highlight the sedimentary dynamics in terms of pH, redox, and ∑H2S, which were found to be directly related to the tidal phases, the organic matter content, and the seasonal regime within this estuary. Finally, this research demonstrates that geochemical processes may change on short time scales, highlighting the importance of the hydrological regime and tidal pumping on the fluctuations of reducing and sulfidic conditions within Peruvian mangrove sediments. Acknowledgements This study was carried out within the framework of the project BImpacto de la Variabilidad y Cambio Climático en el Ecosistema de Manglares de Tumbes^ supported by the BInternational Development Research Centre (IRDC)^ of Canada under management of the BInstituto Geofísico del Perú (IGP),^ in cooperation with the BInstituto del Mar del Perú (IMARPE)^ and the BUniversidad Peruana Cayetano Heredia (UPCH).^ The authors acknowledge the BCátedra CONCYTEC program^ in BCiencias del Mar^ that funded the Master Program in Marine Sciences at UPCH. Detailed geochemical analyses were supported by the IRDC and IMARPE. AP is supported by the BFondo Nacional de Desarrollo Cientifico Tecnologico y de Innovacion Tecnológica^ (Fondecyt, Peru), through the MAGNET research program. CJS is supported by the Australian Research Council (DE160100443). We would like to thank our colleagues Dr. Ken Takahashi, Ernesto Fernández, Wilson Carhuapoma, Percy Montero, Rubén Alfaro, Manuel Vera, and Dr. Jorge Cardich who provided us with invaluable help.
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