Benthic Photosynthesis Research Articles

Extraction of Dyes from Plant Sources and their application on Cotton and Wool using Mordants

Dyeing is an ancient art, which was practiced during the Bronze Age in Europe. Primitive dyeing techniques included sticking plants to fabric or rubbing crushed pigments into cloth. The methods became more sophisticated over time and techniques were developed using natural dyes from crushed fruits, berries and other plants, which were boiled into the fabric and gave light and water fastness [resistance]. The widely and commercially used synthetic dyes impart strong colors but causes carcinogenicity and inhibition of benthic photosynthesis. Hence, use of natural dyes have become an importance in today’s world. In this study, Natural dyes have been extracted from different plant sources namely, Beeta Vulgaris (Beetroot), Spinacia oleracea (Spinach), Ixora coccinea (Jungle Geranium), Brassica oleracea var. capitata f. rubra (Purple Cabbage), and Tagetes erecta (African Marigold) using mordants like FeSO4 and CuSO4 On Cotton and Wool. It was seen that Wool takes up the dye better than cotton because vegetable fibers like cotton take up less dye than animal fibers like wool and CuSO4 is a better mordant than FeSO4.

Nitrogen cycling in muddy sediments of Great Peconic Bay, USA: Seasonal N reaction balances and multi-year flux patterns

To better understand the capacity of sediments to serve as both source and sink of nitrogen (N) and to identify any evidence of evolving changes in sedimentary N cycling, N2production, N remineralization, and N2fixation were studied over a multi-year period (2010–2015) in bioturbated mud of Great Peconic Bay, a temperate northeastern U. S. estuary. Benthic fluxes and rates of organic matter remineralization were measured using in situ and ex situ incubations. Net annual NH+4, NO–3/NO–2, and N2–N fluxes (μ = 1.1, 0.03, and 1.2 mmol m–2d–1) were close to averages for comparable sedi- mentary environments from surveys of published field studies. Net N2fluxes (by membrane inlet mass spectrometry) were influenced in different periods by temperature, oxygenation of sediment, pulsed Corg, and the activity of benthic macrofauna and benthic microalgae, although no single physical or biogeochemical variable showed a strong, direct relationship with net N2fluxes over all sampling periods. In situ measurements sometimes showed more dynamic and higher amplitude diurnal N flux cycles than did ex situ incubations, suggesting ex situ incubations did not fully capture impacts of bioirrigation or benthic photosynthesis.15N tracer experiments indicated anammox was < 7% of total N2production. Acetylene reduction assays demonstrated C2H4production to depths ≥ 15 cm and suggested N2fixation may have approached 25% of gross N2production(3:1 C2H4: N2). Mass balances incorporating independently measured N remineralization estimates were consistent with measured levels of N2fixation. Overall, complex balances of competing processes governed sedimentary N cycling seasonally, and N2production dominated N2fixation. Measured N2fixation was consistent with constraints from N remineralization rates and net N fluxes except in episodic conditions (e. g., algal blooms). There was no indication of progressive changes in N cycling magnitudes or relative N reaction balances over the study period.

Effects of warming and CO2 enrichment on O2 consumption, porewater oxygenation and pH of subtidal silt sediment

We investigated the effects of seawater warming and CO2 enrichment on the microbial community metabolism (using O2 consumption as a proxy) in subtidal silt sediment. Intact sediment cores, without large dwelling infauna, were incubated for 24 days at 12 (in situ) and 18 °C to confirm the expected temperature response. We then enriched the seawater overlying a subset of cold and warm-incubated cores with CO2 (+ ΔpCO2: 253–396 µatm) for 16 days and measured the metabolic response. Warming increased the depth-integrated volume-specific O2 consumption (Rvol), the maximum in the volume-specific O2 consumption at the bottom of the oxic zone (Rvol,bmax) and the volume-specific net O2 production (Pn,vol), and decreased the O2 penetration depth (O2-pd) and the depth of Rvol,bmax (depthbmax). Benthic photosynthesis oscillated the pH in the upper 2 mm of the sediment. CO2 enrichment of the warm seawater did not alter this oscillation but shifted the pH profile towards acidity; the effect was greatest at the surface and decreased to a depth of 12 mm. Confoundment rendered the CO2 treatment of the cold seawater inconclusive. In warm seawater, we found no statistically clear effect of CO2 enrichment on Rvol, Rvol,bmax, Pn,vol, O2-pd, or depthbmax and therefore suspect that this perturbation did not alter the microbial community metabolism. This confirms the conclusion from experiments with other, contrasting types of sediment.

Shallow Salt Marsh Tidal Ponds–An Environment With Extreme Oxygen Dynamics

In marshes, tidal ponds are increasing in number and areal coverage. Getting a better understanding of their unique biogeochemistry is a prerequisite for foreseeing their future role in salt marsh ecosystems. Using in situ microprofiling, this study investigated the spatiotemporal dynamics of O2, pH and CO2 in shallow salt marsh tidal ponds in the summer time. High benthic photosynthetic activity, fueled by CO2 from the sediment, resulted in steep vertical O2 gradients at the sediment-water interface, increasing from anoxia to extremely supersaturated peak concentrations up to 886±139 µmol L-1 (391% atmospheric O2 saturation) over a short distance of 6mm. These characteristic peaks developed even at low light conditions down to 150 µmol m-2 sec-1 photosynthetically active radiation (PAR). The oxygen gradients were restricted to the layer of benthic microalgae on the sediment surface and did not extend into the water column, which was well-mixed throughout the day showing no vertical variation. The benthic photosynthesis and respiration controlled the oxygen concentration in the water column, creating net supersaturated conditions during the day and hypoxic conditions at night. The tidal ponds were generally well-buffered showing only attenuated pH fluctuations ranging from 6.2 to 7.3, and no persistent gradients built up, despite the high photosynthetic activity at the sediment water interface. CO2 accumulated in the sediment and was present in the water column during the morning hours, but depleted in the afternoon due to the high photosynthetic uptake. Tidal ponds also experienced event-driven changes in their biogeochemistry. Sea foam developed on the water surface during the day and accumulated on one side of the pond blocking light penetration and lowering oxygen concentrations under the foam. Inundation at high tide caused a short-lived temporal variation in O2 and pH, which was restricted to the time of the flood. As the flooding water receded, the preceding O2 and pH conditions were immediately restored. Altogether shallow tidal ponds comprise a marsh habitat with distinctive spatiotemporal oxygen dynamics driven by benthic photosynthesis and respiration, which differ from the surrounding vegetated marsh, and could drive changes in salt marsh biogeochemistry in response to increased pond coverage.

On diel variability of marine sediment backscattering properties caused by microphytobenthos photosynthesis: Impact of environmental factors

Abstract The study has been motivated by the development of the hydroacoustic techniques for mapping and classifying the benthic habitats and for the research of the microbenthos photosynthesis in the semi-enclosed Baltic Sea, particularly sensitive to human activity. The investigation of the effect of the benthic microalgal photosynthesis on the echo signal from the Baltic sandy sediments is continuing. The study clarifies the impact of the abiotic and biotic factors on the diel variation of the backscattering caused by the benthic microalgal photosynthetic activity. Five multiday laboratory experiments, different in hydrophysical or biological conditions, were conducted. During each measurement series, the “day” (illumination) and “night” (darkness) conditions (L:D cycle) were simulated and the diel variations of the echo energy of the backscattered signal were analyzed. The hydroacoustic data were acquired along with measuring biological and biooptical parameters and oxygen concentration. The study demonstrated the impact of microphytobenthos photosynthesis on the backscattering properties of the marine sediment which is sensitive to the illumination level, benthic microalgal biomass and macrozoobenthos bioturbation.

Effects of CO2 enrichment on benthic primary production and inorganic nitrogen fluxes in two coastal sediments

Ocean acidification may alter the cycling of nitrogen in coastal sediment and so the sediment–seawater nitrogen flux, an important driver of pelagic productivity. To investigate how this perturbation affects the fluxes of NOX− (nitrite/nitrate), NH4+ and O2, we incubated estuarine sand and subtidal silt in recirculating seawater with a CO2-adjusted pH of 8.1 and 7.9. During a 41-day incubation, the seawater kept at pH 8.1 lost 97% of its NOX− content but the seawater kept at pH 7.9 lost only 18%. Excess CO2 increased benthic photosynthesis. In the silt, this was accompanied by a reversal of the initial NOX− efflux into influx. The estuarine sand sustained its initial NOX− influx but, by the end of the incubation, released more NH4+ at pH 7.9 than at pH 8.1. We hypothesise that these effects share a common cause; excess CO2 increased the growth of benthic microalgae and so nutrient competition with ammonia oxidising bacteria (AOB). In the silt, diatoms likely outcompeted AOB for NH4+ and photosynthesis increased the dark/light fluctuations in the pore water oxygenation inhibiting nitrification and coupled nitrification/denitrification. If this is correct, then excess CO2 may lead to retention of inorganic nitrogen adding to the pressures of increasing coastal eutrophication.

Metabolismo líquido da matéria orgânica, calcificação e fluxos de dióxido de carbono em dois recifes costeiros sujeitos a diferentes graus de impacto: Coroa Vermelha e Taipus de Fora, Bahia

This study intended to compare physical and chemical variables, net ecosystem metabolism (production – respiration) and calcification-carbonate dissolution rates in two coastal reefs subject to different levels of anthropogenic inputs of nutrients and organic matter. The coast surrounding Coroa Vermelha reef presented a higher degree of urbanization and touristic activities than Taipus de Fora at the time of sampling. The temperature, dissolved inorganic nutrients, total alkalinity, and total suspended solids were significantly higher in Coroa Vermelha reef, probably as a result of the anthropogenic inputs. These variables in Taipus de Fora were comparable to those found in the literature for Recife de Fora, an offshore protected reef and other less impacted reefs. Total alkalinity, dissolved inorganic carbon and carbon dioxide partial pressure were lower and pH was higher in the reef flat than at the surrounding seawater. There was a prevalence of an influx of atmospheric carbon dioxide to reef water, net autotrophy and calcification. A significant correlation was observed between net calcification and net community metabolism. The benthic photosynthesis in the reef flat during low tide decreases the carbon dioxide partial pressure and increases the aragonite saturation state, establishing thermodynamic conditions that favor calcification.

Seasonal rates of benthic primary production in a Greenland fjord measured by aquatic eddy correlation

We present the first year‐round estimates of benthic primary production at four contrasting shallow (3–22 m depth) benthic habitats in a southwest Greenland fjord. In situ measurements were performed using the noninvasive aquatic eddy‐correlation (EC) oxygen (O2) flux method. A series of high‐quality multiple‐day EC data sets document the presence of a year‐round productive benthic phototrophic community. The shallow‐water sites were on average autotrophic during the spring and summer months, up to 43.6 mmol O2 m−2 d−1, and heterotrophic or close to metabolic balance during the autumn and winter. Substantial benthic gross primary production (GPP) was measured year‐round. The highest GPP rates were measured during the spring, up to 5.7 mmol O2 m−2 h−1 (136.8 mmol O2 m−2 d−1), and even at low light levels (< 80 µmol quanta m−2 s−1) during late autumn and winter we measured rates of up to 1.8 mmol O2 m−2 h−1 (43.2 mmol O2 m−2 d−1) during peak irradiance. The benthic phototrophic communities responded seasonally to ambient light levels and exhibited year‐round high photosynthetic efficiency. In situ downwelling irradiances as low as ∼ 2 µmol quanta m−2 s−1 induced an autotrophic response and light saturation indices (Ik) were as low as 11 µmol quanta m−2 s−1 in the winter. On an annual timescale, the average areal rate of benthic GPP was 11.5 mol O2 m−2 yr−1, which is ∼ 1.4 times higher than the integrated gross pelagic primary production of the ∼ 30–50 m deep photic zone of the fjord. These results document the importance of benthic photosynthesis on an ecosystem level and indicate that the benthic phototrophic compartment should be accounted for when assessing carbon and nutrient budgets as well as responses of coastal Arctic ecosystems to climate change.

Potential for large-bodied zooplankton and dreissenids to alter the productivity and autotrophic structure of lakes.

While limnological studies have emphasized the importance of grazers on algal biomass and primary production in pelagic habitats, few studies have examined their potential role in altering total ecosystem primary production and it's partitioning between pelagic and benthic habitats. We modified an existing ecosystem production model to include biotic feedbacks associated with two groups of large-bodied grazers of phytoplankton (large-bodied zooplankton and dreissenid mussels) and estimated their effects on total ecosystem production (TEP), and the partitioning of TEP between phytoplankton and periphyton (autotrophic structure) across large gradients in lake size and total phosphorus (TP) concentration. Model results indicated that these filter feeders were capable of reducing whole-lake phytoplankton production by 20-70%, and increasing whole-lake benthic production between 0% and 600%. Grazer effects on TEP were constrained by lake size, trophic status, and potential feedbacks between grazing and maximum rates of benthic photosynthesis (BP(MAX)). In small (mean depth Z < 10 m) oligotrophic and mesotrophic (TP < 100 mg P/m2) lakes, both large-bodied zooplankton and dreissenids were capable of increasing the benthic fraction (Bf) by 10-50% of TEP. Small lakes were also the only systems where TEP had the potential to increase in the presence of large-bodied grazers, but such increases only occurred if grazer-induced changes in water clarity, macrophyte coverage, or nutrient availability stimulated specific growth rates of periphyton. In other scenarios, TEP declined by a maximum of 50%. In very large lakes (Z > 100 m), Bf was minor (< 10%) in the presence or absence of grazers, but increases in littoral habitat and the stimulation of benthic production in these ecosystems could be of ecological relevance because littoral zones in large lakes contain a relatively high proportion of within-lake biodiversity and are important for whole-lake food webs.

Measurement of benthic photosynthesis and calcification in flowing‐through seawater with stable carbonate chemistry

Estimation of photosynthetic or calcification rates of benthic organisms under stable seawater chemistry is important to fathom their capacity of CO2 fixation under constant or controlled levels of pCO2 and acidity of seawater. The flowing‐through system, introduced here, can hold large individuals or colonies and maintain the carbonate chemical parameters stable while photosynthetic or calcification rate is measured based on the assimilation pipe inlet and outlet differences in dissolved O2 concentrations or total alkalinity. The data obtained with this system for macroalgae showed constancy over time under controlled conditions, resulting in higher photosynthetic rates compared with those measured in a closed mode, which caused significant changes in the carbonate system (decreased pCO2 and DIC and increased pH). When the method was applied to measurements of calcification based on the changes in total alkalinity, reliable data were obtained for both coralline algae and oysters. In addition, it can also be applied to measure respiration of both macrophyte and animals and to test the effects of increased pCO2 and current speeds when these factors are controlled under either laboratory or field conditions while exposed to natural solar radiation.

The influence of pore‐water advection, benthic photosynthesis, and respiration on calcium carbonate dynamics in reef sands

To investigate diel calcium carbonate (CaCO3) dynamics in permeable coral reef sands, we measured pore‐water profiles and fluxes of oxygen (O2), nutrients, pH, calcium (Ca2+), and alkalinity (TA) across the sediment‐water interface in sands of different permeability at Heron Reef, Australia. Background flushing rates were high, most likely as a result of infaunal burrow irrigation, but flux chamber stirring enhanced pore‐water exchange. Light and pore‐water advection fueled high rates of benthic primary production and calcification in sunlit surface sediments. In the light, benthic photosynthesis and calcification induced surface minima in Ca2+ and TA and peaks in pH and O2. Oxygen penetration depth in coarse sands decreased from ∼ 1.2 cm during the day to ∼ 0.6 cm at night. Total oxygen uptake (TOU) in dark chambers was three to fourteen times greater than diffusive uptake and showed a direct effect of pore‐water advection. Greater sediment oxygen consumption rates were observed in higher permeability sands. In the dark, TA release was not stimulated by increasing TOU because of a damping effect of pore‐water advection on metabolic CaCO3 dissolution efficiency. On a daily basis, CaCO3 undergoes net dissolution in Heron Reef sands. However, pore‐water advection can reverse the CaCO3 budget and promote CaCO3 preservation under the most energetic conditions.

남해안 주요 하구 갯벌 퇴적물의 탈질소화를 통한 질소 영양염 제거

남해안의 주요 하구 4곳(순천만, 섬진강, 고성천, 마산만)과 서해안의 태안 근소만 갯벌에서 2009년 3월부터 2010년 5월까지 유기물 정화능력을 파악할 수 있는 퇴적물 산소요구량(Sediment Oxygen Demand; SOD)과 탈질소화(Denitrification)를 측정하였다. 퇴적물 산소요구량은 퇴적물 배양 중 시간당 용존산소감소율로 부터 추정되었으며, 탈질소화 측정에는 질소 안정동위원소를 추적자로 이용하는 isotope paring technique이 사용되었다. 조사지역의 퇴적물 산소요구량과 탈질소화율은 각각 -5.1~24.6 mmole <TEX>$O_2m^{-2}d^{-1}$</TEX>와 0.0~3.9 mmole <TEX>$N_2m^{-2}d^{-1}$</TEX>의 범위를 보였다. 퇴적물 산소요구량이 가장 높은 곳은 마산만(평균 = 10.2(범위 =-2.2~19.2 mmole <TEX>$O_2m^{-2}d^{-1}$</TEX>)이었으며, 순천만, 고성, 태안, 섬진강 순으로 나타났다. 탈질소화율도 마산만(평균 = 1.0(범위 =0.0~3.9) mmole <TEX>$N_2 m^{-2}d^{-1}$</TEX>이 가장 높았으며, 고성, 섬진강, 순천만, 태안 순으로 나타났다. 태안, 섬진강, 마산 지역에서는 계절적으로 저서미세조류에 의한 광합성이 탈질소화에 뚜렷한 영향을 미쳤는데 광합성 동안 생성된 산소는 혐기성과정인 탈질소화를 저해하기 보다는 질산화를 원활하게 하여, 질산화-탈질소화 연계과정을 촉진시켰다. 남해안 허구에서 탈질소화의 계절변화 유형(봄철 최대 유형과 여름철 최대 유형)의 지역적 차이는 탈질소화에 사용되는 두 질산원(<TEX>$D_w$</TEX>; 강을 통해 공급된 질산과 <TEX>$D_n$</TEX>; 질산화-탈질소화 연계과정에 의해 생성된 질산)의 상대적 중요성에 따라 결정되었다. 즉 봄철에 탈질소화가 높게 나타난 순천만, 고성, 마산은 여름철에 비해 봄철 수층 질산염이 풍부하였고, 이를 통해 <TEX>$D_w$</TEX>가 증가되었다. 태안과 섬진강 지역이 여름철에 탈질소화 최대값을 보인 이유는 수층의 질산염이 고갈되지 않은 상태에서 여름철 수온의 증가로 <TEX>$D_w$</TEX>가 증가하였고, 이와 더불어, 산소고갈이 나타나지 않아 질산화에 좋은 환경이 조성되었으며, 결과적으로 <TEX>$D_n$</TEX>이 증가되었기 때문이다. Sediment oxygen demand(SOD) and denitrification rates were measured in four major estuaries(Suncheon Bay, Seomjin river estuary, Goseong stream estuary and Masan Bay) in south coast of Korean peninsula from March of 2009 to May 2010 to estimate organic matter cleaning capacity. SOD was estimated from the temporal dissolved oxygen concentration change and isotopic pairing technique was employed to measure denitrification. Sediment oxygen demand(SOD) was ranged from -5.1 to 24.6 mmole <TEX>$O_2m^{-2}d^{-1}$</TEX> and denitrification rate was ranged from 0.0 to 3.9 mmole <TEX>$N_2m^{-2}d^{-1}$</TEX>in the study area. SOD was the highest in Masan Bay(-2.2 to 19.2, average = 10.2 mmole <TEX>$O_2m^{-2}d^{-1}$</TEX>) and Suncheon, Goseong, Tae-an and Seomjin followed. Denitrification was also the highest in Masn Bay(0.0 to 3.9, average = 1.0 mmole <TEX>$N_2m^{-2}d^{-1}$</TEX>) and Goseong, Seomjin, Suncheon and Taean followed. The effect of benthic photosynthesis by microphytobenthos on denitrification was evident in some season of Tae-an, Seomjin, and Masn Bay. The increased oxygen level produced by photosynthesis stimulated nitrification without severe adverse effect on denitrification and, as a result, coupled nitrification and denitrification was enhanced in these areas. A difference of seasonal patterns of denitrification at each site depended on relative importance of denitrification on different nitrate source(<TEX>$D_w$</TEX>: nitrate from water column and <TEX>$D_n$</TEX>: nitrated produced during nitrification). Denitrification was maximum during spring in Goseong, Suncheon and Masan Bay. On the contrary, denitrification was the highest during summer in Tae-an and Seomjin estuary.

Contamination on sandflats and the decoupling of linked ecological functions

AbstractBenthic macrofauna can influence inputs and transformations of energy and matter in estuaries, affecting both the stocks of vital materials (e.g. carbon, oxygen) and the rates of key processes (e.g. organic matter decomposition, nutrient uptake). Although a number of studies have identified shifts in functional groups or biological traits in relation to anthropogenic stressors, there have been few field‐based assessments of changes in functioning associated with stress gradients. We used a comparative experimental approach to investigate functioning on two sandflats with differing exposures to urban contaminants. Apart from significant differences in sediment contaminant concentrations (43.2 ± 1.8 mg kg−1Zn and 15.6 ± 0.9 mg kg−1Pb at the Pollen site; 17.7 ± 0.7 mg kg−1Zn and 7.9 ± 0.9 mg kg−1Pb at the Waiheke site), the two sandflats were readily comparable: both had similar sediment grain size distributions and were dominated by the same macrofaunal species; and both were in non‐eutrophic New Zealand marine reserves with low ambient sediment organic matter content. To better understand the effects of contaminants on biologically mediated transformations of organic matter into inorganic nutrients, we manipulated sediment organic matter content and macrofaunal abundance in standardized treatments at each site. Fluxes of oxygen and ammonium, which are linked to key sandflat processes such as organic matter decomposition and benthic photosynthesis, were measured as response variables 1 week after the experimental manipulations. We predicted more efficient organic matter processing on the uncontaminated flat and thus expected to see elevated ammonium efflux in response to organic enrichment treatments at this site. Higher rates of benthic photosynthesis were predicted for plots with higher ammonium efflux, as ammonium is a readily utilizable form of limiting inorganic nitrogen. We documented significant positive relationships between ammonium uptake and benthic primary production on the uncontaminated flat, but weaker/insignificant relationships at the contaminated site. Our data were consistent with theories of increased variability and a decoupling of system processes with increasing amounts of stress.

Summer-winter transitions in Antarctic ponds II: Biological responses

AbstractWe observed ice formation and water column attributes in four shallow Antarctic ponds between January and 7 April 2008. During that time ponds went from ice-free to &gt; 80 cm thick ice, near-freshwater to hypersaline, well-lit to near darkness and temperatures fell to below zero. Here we examine shifts in biological activity that accompanied these changes. During February, freeze-concentration and ongoing photosynthesis increased dissolved oxygen concentration to up to 100 mg l-1, with a near-equivalent decrease in dissolved inorganic carbon and a pH rise. Benthic photosynthesis was responsible for 99% of estimated biological oxygen production. Net oxygen accumulation ceased in late February, pH began to fall and inorganic carbon to increase, but the pool of dissolved oxygen was depleted only slowly. Anoxia had been attained in only one pond by April and there was little accumulation of indicators of anaerobic activity. The nitrogen and phosphorus balances of the ponds were dominated by organic forms, which, like DOC and CDOM, behaved conservatively. Conversely, inorganic nitrogen and phosphorus uptake was evident throughout the study period, at a molar ratio of 16N:1P in two of three ponds, consistent with uptake into biological material. We found no coupling between N and P uptake and photosynthesis.

Effects of climate on organic carbon and the ratio of planktonic to benthic primary producers in a subarctic lake during the past 45 years

The effects of climatic variables on lake‐water total organic carbon (TOC) concentrations and benthic and pelagic primary producers during the past 45 yr were assessed using the sediment records of two subarctic lakes, one with mires and one without mires connected to the lake. The lake with a mire showed large and synchronous changes in the planktonic to benthic (P : B) ratio of diatoms and concentrations of TOC inferred from nearinfrared spectroscopy. During periods of warm temperatures, high precipitation, and long ice‐free conditions, we inferred high TOC in the lake, and the diatom community was dominated by planktonic species. The stable carbon isotopic (Δ13C) values of sediment organic matter were negatively correlated with inferred TOC concentration and P :B ratio. We suggest that the changes in TOC and P : B ratio were a result of changing climate, permafrost degradation, and related changes in the catchment. Terrestrial organic matter, by its strong effect on the penetration of light through the lake water, possibly affected the habitats available for benthic photosynthesis and thus the Δ13C of the sediment organic matter. The large changes in recent times may also be because of unusually long ice‐free periods, warmer temperatures, and other associated limnological changes. The lake with no mire next to the lake showed only minor changes in lake‐water TOC during the same period and P :B ratio remained almost constant until the past 5 yr, when the P :B ratio increased rapidly. The observed changes in P :B ratio within this lake may be because of complex interactions of several climate‐related variables.

Measurement of acid polysaccharides (APS) associated with microphytobenthos in salt marsh sediments

Microphytobenthos (MPB) are an important component of shallow-water habitats where there is sufficient light to support benthic photosynthesis. Production of extracellular poly- meric substances (EPS) is characteristic of the MPB, and acid polysaccharides (APS) are a major com- ponent of these EPS. A simple technique was developed to extract and measure APS concentrations in sediments. Water-extractable APS (wAPS) were extracted with ultra high purity water from lyophilized sediments. After centrifuging to remove the sediment, wAPS in the supernatant was precipitated with alcian blue, a cationic dye. The APS-alcian blue precipitate was removed by filtra- tion. The remaining alcian blue in solution was determined spectrophotometrically and was inversely proportional to the concentration of wAPS in the sediment. Chlorophyll (chl) a, carbohydrate frac- tions, and wAPS were measured in sediments from 5 contrasting sites in a microtidal salt marsh in the subtropics. wAPS concentrations, expressed as gum xanthan equivalents, ranged from 152 to 6268 mg m -2 in the upper 5 mm of sediment. The biomass (determined as chl a) of MPB at all sites was highest in the winter compared to the summer. There was a significant correlation (r = 0.675, p < 0.001, n = 107) between sediment wAPS and chl a concentrations. The ratio of wAPS to saline- extractable EPS (sEPS) was significantly higher in summer compared to winter, indicating a seasonal change in the composition of EPS. These data show that APS are a significant and variable compo- nent of the EPS pool in salt marsh sediments.

BENTHIC ALGAL PRODUCTION ACROSS LAKE SIZE GRADIENTS: INTERACTIONS AMONG MORPHOMETRY, NUTRIENTS, AND LIGHT

Attached algae play a minor role in conceptual and empirical models of lake ecosystem function but paradoxically form the energetic base of food webs that support a wide variety of fishes. To explore the apparent mismatch between perceived limits on contributions of periphyton to whole-lake primary production and its importance to consumers, we modeled the contribution of periphyton to whole-ecosystem primary production across lake size, shape, and nutrient gradients. The distribution of available benthic habitat for periphyton is influenced by the ratio of mean depth to maximum depth (DR = z/ z(max)). We modeled total phytoplankton production from water-column nutrient availability, z, and light. Periphyton production was a function of light-saturated photosynthesis (BPmax) and light availability at depth. The model demonstrated that depth ratio (DR) and light attenuation strongly determined the maximum possible contribution of benthic algae to lake production, and the benthic proportion of whole-lake primary production (BPf) declined with increasing nutrients. Shallow lakes (z < or =5 m) were insensitive to DR and were dominated by either benthic or pelagic primary productivity depending on trophic status. Moderately deep oligotrophic lakes had substantial contributions by benthic primary productivity at low depth ratios and when maximum benthic photosynthesis was moderate or high. Extremely large, deep lakes always had low fractional contributions of benthic primary production. An analysis of the world's largest lakes showed that the shapes of natural lakes shift increasingly toward lower depth ratios with increasing depth, maximizing the potential importance of littoral primary production in large-lake food webs. The repeatedly demonstrated importance of periphyton to lake food webs may reflect the combination of low depth ratios and high light penetration characteristic of large, oligotrophic lakes that in turn lead to substantial contributions of periphyton to autochthonous production.

Effects of spatangoid heart urchins on O2 supply into coastal sediment

Spatangoid heart urchins are key bioturbators in the marine environment. They pump seawater from the sediment surface around their tests and, at the same time, constantly displace the surrounding sediment. To improve our understanding of the effects of this activity on the oxygena- tion of coastal sediment, we studied for the first time in situ (O2) around Echinocardium cordatum at sub-millimeter resolution under different hydraulic conditions. In the laboratory, we investigated the effects of E. cordatum on pore-water pH and sediment apparent diffusivity. Individuals advancing 1 to 3 cm h -1 through the upper 4 cm of the sediment displaced a greater volume of seawater than sediment per unit time. The O2 uptake of the sediment surrounding E. cordatum was at least twice the respiration of the echinoids. Besides creating additional sediment contact with oxygenated sea- water, E. cordatum affected the supply of O2 to the sediment by altering photosynthetic O2 produc- tion at the sediment surface, and increasing the exchange area of the sediment-seawater interface and apparent diffusivity of the uppermost sediment layer. After the passage of an individual, pore- water (O2) profiles indicative of benthic photosynthesis recovered rapidly from the disturbance, but the pH of deeper pore water was altered. In situ, time series measurements of (O2) and hydrostatic pressure indicated that wind waves can increase the transport of O2 across both the sediment- seawater interface and the interface between the seawater surrounding E. cordatum and the adjacent sediment.

Benthic photosynthesis in submerged Wadden Sea intertidal flats

In this study we compare benthic photosynthesis during inundation in coarse sand, fine sand, and mixed sediment (sand/mud) intertidal flats in the German Wadden Sea. In situ determinations of oxygen-, DIC- and nutrient fluxes in stirred benthic chamber incubations were combined with measurements of sedimentary chlorophyll, incident light intensity at the sediment surface and scalar irradiance within the sediment. During submergence, microphytobenthos was light limited at all study sites as indicated by rapid response of gross photosynthesis to increasing incident light at the sea floor. However, depth integrated scalar irradiance was 2 to 3 times higher in the sands than in the mud. Consequently, gross photosynthesis in the net autotrophic fine sand and coarse sand flats during inundation was on average 4 and 11 times higher than in the net heterotrophic mud flat, despite higher total chlorophyll concentration in mud. Benthic photosynthesis may be enhanced in intertidal sands during inundation due to: (1) higher light availability to the microphytobenthos in the sands compared to muds, (2) more efficient transport of photosynthesis-limiting solutes to the microalgae with pore water flows in the permeable sands, and (3) more active metabolic state and different life strategies of microphytobenthos inhabiting sands.

Spatial and temporal patterns of mineralization rates and oxygen distribution in a permeable intertidal sand flat (Sylt, Germany)

Oxygen distribution and benthic mineralization rates were investigated in a permeable intertidal sand flat (permeability: 3.9 x 10‐11 m2) in a transect from the low toward the high waterline. At all stations, oxygen penetrated several millimeters to centimeters into the sediments during inundation because of pore‐water advection. The wave‐ and current‐driven deep oxygen penetration caused high oxygen consumption rates (OCRs) and high aerobic mineralization rates at all stations. Because oxygen penetration was enhanced during inundation, 71‐90% of the daily oxygen consumption took place in that period. OCRs and sulfate reduction rates (SRRs) changed with inundation time of the stations, emphasizing the importance of pore‐water advection for benthic mineralization: OCRs were elevated at the lower flat in summer (lower flat 131‐187; middle and upper flat 64‐108 mmol C m‐2 d‐1). SRRs increased sharply from the high to the low waterline during all seasons (e.g., in summer: lower flat 18‐40; middle flat 8.8‐9.4, upper flat 0.5‐4 mmol C m‐2 d‐1). A one‐dimensional model of the advective organic matter supply to the sediment could only explain a fraction of the organic carbon required for benthic mineralization. This suggests that either transport of particles via the seawater is more efficient than the one‐dimensional concept can explain or that additional carbon was supplied through other sources (e.g., benthic photosynthesis). Mineralization rates were higher in summer than in winter. Only in summer did sulfate reduction contribute ≫20% to total mineralization.