Dissolved Oxygen Deficit Research Articles

Evaluation of the operation of the stabilization pond for agricultural irrigation purposes

Improving the quality of residual water and increasing agricultural production is necessary to achieve food sovereignty in water deficit conditions. The research was carried out to evaluate the operation of the precision lagoon for agricultural irrigation purposes by determining the geometric and hydraulic parameters, kinetic coefficients and dissolved Oxygen using the Streeter & Phelps model. The main results indicate the presence of a facultative lagoon with a hydraulic retention time of 6.7 days, flow rate of 1 641,6 m3 day-1 contributed by 41 312 inhabitants, solar penetration of 0.20 m, presence of green algae, 0,36 day-1 deoxygenation coefficient, 0,60 day-1 reaeration coefficient, 0,09 day-1 sedimentation coefficient, 0,45 day-1 total removal coefficient, dissolved Oxygen of the effluent of 2 mg L-1, initial dissolved oxygen deficit of the influent and effluent of 8,4 mg L-1 and 2,43 mg L-1 respectively. These indicate that the effluents can be used as wastewater reuse for irrigation of cooked food crops according to the recommendations of the World Health Organization. Keywords: wastewater, kinetic coefficients, dissolved Oxygen, hydraulic parameters, reuse.

Potential Impact of Climate Change on Mineralization and Main Ions Ratio in Surface Fresh Waters (a Review)

The article deals with problem of the fresh waters salinization in view of its relevance for normal functioning of the aquatic ecosystems, development of different branches of industry and agriculture, and human health. Attention is focused on the fact that the fresh waters' salinization inevitably results in decrease of the ecosystem services scope. The main factors and anthropogenic sources of influence on total dissolved solids in the fresh waters and metamorphosis of their ion composition are considered. It is stated that climate changes potentially affect and will affect the surface waters mineralization in future owing to volume and frequency of the atmospheric precipitation, intensity of the rocks and minerals weathering, the ground feeding of the rivers, the marine water penetration into the estuaries along with reducing of the river water yield, etc. The possible impact of mineralization changes on migration of substances from bottom sediments into the water thickness, that is on the intensity of its secondary pollution, is discussed. This impact can be direct and indirect. First of all, it concerns the migration ability of metals in bottom sediments. Elevated content of Na<sup>+</sup>, Ca<sup>2+</sup> and Mg<sup>2+</sup> in water intensifies migration of metals of the exchangeable fraction of bottom sediments. The indirect effect of elevated mineralization is expressed in the oxygen regime of the water bodies, which usually deteriorates in the near-bottom water layers of deep lakes and reservoirs, mouth areas of the rivers and estuaries. The dissolved oxygen deficit becomes usual, anoxic conditions are formed, which favor release of Fe(III) and Mn(IV) from oxyhydroxides or the oxide fraction of the bottom sediments. A review also considers some aspects of potential impact of the fresh waters salinization on survival of the aquatic plants and animals and biodiversity.

Effects of COVID-19 lockdown on water quality, microbial extracellular enzyme activity, and sediment-P release in the Ganga River, India.

This study investigates possible improvement in water quality and ecosystem functions in the Ganga River as influenced by COVID-19 lockdown in India. A total of 132 samples were collected during summer-2020 low flow (coinciding COVID-19 lockdown) for water (sub-surface and sediment-water interface) and 132 samples separately for sediment (river bottom and land-water interface) considering 518-km main river stem including three-point sources (one releases urban sewage and the other two add metal-rich industrial effluents) and a pollution-impacted tributary. Parameters such as dissolved oxygen deficit and the concentrations of carbon, nutrients (N and P), and heavy metals were measured in water. Sediment P-release was measured in bottom sediment whereas extracellular enzymes (EE; alkaline phosphatase, FDAase, protease, and β-D-glucosidase) and CO2 emission were measured at land-water interface to evaluate changes in water quality and ecosystem functions. The data comparisons were made with preceding year (2019) measurements. Sediment-P release and the concentrations of carbon, nutrients, and heavy metals declined significantly (p<0.05) in 2020 compared to those recorded in 2019. Unlike the preceding year, we did not observe benthic hypoxia (DO <2.0 mg L−1) in 2020 even at the most polluted site. The EE activities, which declined sharply in the year 2019, showed improvement during the 2020. The stability coefficient and correlative evidences also showed a large improvement in the water quality and functional variables. Positive changes in functional attributes indicated a transient recovery when human perturbations withdrawn. The study suggests that timing the ecosystem recovery windows, as observed here, may help taking management decision to design mitigation actions for rivers to recover from anthropogenic perturbations.

ASSESSMENT OF RIVER WATER QUALITY IN THE CITY BY HYDROCHEMICAL INDICES (THE OKHTA RIVER, ST. PETERSBURG)

The Okhta River water quality was assessed in the period 2016–2020 using the component- wise assessment method and three hydrochemical indices (Water Pollution Index (WPI), Specific Combinatorial Water Pollution Index (SCWPI), and Canadian Council of Ministers of the Environment Water Quality Index (CCME WQI)). The component-wise assessment demonstrated that the pH was neutral or slightly alkaline, and water hardness was low. Dissolved oxygen deficit was observed at most stations during the entire research period. The content of dissolved oxygen declined downstream along the river. At the river mouth, the oxygen situation is slightly better due to the inflow of the Neva River water. The BOD5 exceeded the MPC at all sampling stations, suggesting the Okhta River water was polluted with readily oxidizable organic matter. The iron content in the water exceeded the MPC manifold. An elevated content of various forms of nitrogen was also revealed. Over the entire observation period, increased concentrations of oil products were constantly recorded (exceeding MPC more than 50‑fold in different years). The Okhta River water was characterized as “dirty” and “extremely dirty”, and the water quality was “poor” according to the calculated values of the indices – WPI, SCWPI and CCME WQI. The methodology of the little-known in Russia CCME WQI is considered separately. It was compared with the WPI and SCWPI. The relationship between the indices is clarified. The use of CCME WQI for surface water quality assessment along with SCWPI is recommended.

Trends, insights and effects of the Urban Wastewater Treatment Directive (91/271/EEC) implementation in the light of the Polish coastal zone eutrophication

The intensification of the Baltic Sea eutrophication is associated with the increase of anthropogenic nutrients loads, mainly nitrogen and phosphorus introduced into surface waters from a diffuse, point and natural background sources. Despite the observed decreasing trends in nutrient concentrations in some parts of the Baltic Sea, eutrophication-related indicators continue to deteriorate. This accelerates harmful algal blooms and dissolved oxygen deficits resulting in severe ecosystem disturbance. The paper presents trends, insights and effects of the Urban Wastewater Treatment Directive 91/271/EEC implementation in Poland based on the nutrient riverine loads from Polish territory with particular attention given to the development of municipal wastewater treatment plants under the National Wastewater Treatment Programme 2003–2016. Environmental effects of wastewater infrastructure modernisation are investigated by using available data on the changing nutrient concentrations in the coastal water in 3 basins (Gdansk Basin, Bornholm Basin and Eastern Gotland Basin) belonging to the Polish Exclusive Economic Zone within the Baltic Sea. The results show that the decreasing trend regarding phosphorus loads reduction from municipal effluents was achieved while a stable trend with temporary increases was achieved in terms of nitrogen loads. Moreover, the investigation provides information about the potential bioavailability of discharged effluents before and after the Directive implementation by including total and inorganic forms of nitrogen and phosphorus in the analysis.

Dissolved oxygen deficits in a shallow eutrophic aquatic ecosystem (fishpond) – Sediment oxygen demand and water column respiration alternately drive the oxygen regime

Biological processes tend to dominate the oxygen regime of productive waters. However, in shallow aquatic ecosystems, it is unclear whether the oxygen regime is driven by oxygen production and consumption in the water column or by sediment oxygen demand (SOD). In managed eutrophic ecosystems, this question is especially important in the context of extreme daily oscillations of dissolved oxygen (DO) that could breach physiological limits of heterotrophic aerobic organisms. High-frequency measurement of DO, temperature, global radiation (Gl.Rad.), and pH in a 0.6 m deep, 22 ha eutrophic fishpond Rod (Czech Republic) shows that the oxygen regime depended on the ecosystem state. Over the clearwater period in the early season, the DO level reflected ecosystem heterotrophy with relatively low daily DO oscillations. However, during the summer phytoplankton bloom, the fishpond was primarily autotrophic with extreme DO fluctuation. During late summer, a collapse of the phytoplankton bloom and an associated shift towards heterotrophy and DO deficit frequently occur. In-situ mesocosm experiments in Rod fishpond were conducted throughout 2018 and 2019 growing seasons, to address the importance of SOD to the oxygen regime. We enclosed the water column in transparent and opaque/dark plastic cylinders open or closed to the sediment. The results show that the proportional contribution of SOD to total respiration decreased from 70 to 90% at low phytoplankton biomass (expressed as Chlorophyll-a (Chl-a) concentration) to approximately 10% at phytoplankton bloom. At night, the difference between the oxygen consumption in the cylinders with or without sediment was statistically significant, when the concentration of Chl-a was <100 μg·L−1. On the contrary, the difference was not significant when the concentration of Chl-a was >100 μg·L−1. This revealed that the impact of SOD is negligible at high phytoplankton biomass.

Anthropogenically enhanced sediment oxygen demand creates mosaic of oxygen deficient zones in the Ganga River: Implications for river health

Dissolved oxygen (DO) plays a major role in sustaining aquatic communities; its concentration and regulatory determinants are considered a key node predicting eutrophy, ecosystem health, and biogeochemical feedbacks. Here we report the status of dissolved oxygen deficit (DOD; hypoxia), and its mechanistic links with sediment oxygen demand (SOD) in the Ganga River. We conducted two independent but interlinked studies during summer low flows of three consecutive years (2016–2018) considering: 1) a 518 km middle segment of the Ganga River between Kanpur upstream and Varanasi downstream; and 2) trajectory analyses downstream two point sources, one flushing industrial effluents (Wazidpur drain) and the other with urban sewage (Assi drain). The concentration of DO at sediment-water interface (DOsw) did appear < 2.0 mg L−1 (hypoxia) at Jjmu; and up to 600 m and 800 m downstream Assi and Wazidpur drain respectively. The DOD at sediment-water interface (DODsw) was highest at Jjmu and did not show a significant decrease up to 300 m downstream to point sources. The SOD which varied between 2.03 and 13.16 (main river stem); 4.39 and 16.81 (Wazidpur drain); and between 2.00 and 13.50 g O2 m−2 d−1 (Assi drain), was found to be a major contributor of DOD. Principal component analysis (PCA) and non-metric multi-dimensional scaling (NMDS) separated DO and alkaline phosphatase (AP) opposite to oxygen-consuming processes and sediment-P release. Using a dynamic fit model, we tested the dependence of sediment-P release on DOsw and DODsw. A large increase in the sediment-P release with increasing DODsw and decreasing DOsw indicated that the system may compromise its resilience in long-term future in terms of self-fertilization and P-eutrophy if the similar magnitude of anthropogenic pressure is continued. The study advances our understanding towards DOD associated habitat fragmentation, ecosystem resilience and niche opportunities useful for recovery and management of the Ganga River.

Composite Goodness of Fit in Reaeration Coeffcient Modeling

Determination of reaeration coefficient is an important factor in surface water quality modeling as it determines the efficiency of the Streeter-Phelps model used for predicting dissolved oxygen deficit of any stream. This study compared the efficiency of Atuwara model with ten other reaeration coefficients models by making use of three data sets obtained from river Atuwara during the prevalent wet and dry seasons using composite goodness of fit test which was developed by quantitatively combining statistical and graphical goodness of fit. The eleven tested models were ranked in order of performance. Results show that the four top ranking models were developed through a process that utilized data from multiple streams while models that were developed from data obtained from the test subject alone performed less competitively. The outcome of the study also suggests that the usual practice of selecting the best model based on statistical analysis alone does not necessarily yield the best result and therefore recommended the incorporation of quantitatively analyzed graphs. The paper concludes that selection of the best performing model among existing reaeration coefficient models using the composite goodness of fit may present a cheaper and better alternative to conventional model development approach.

Anoxia in southern Benguela during the autumn of 2009 and its linkage to a bloom of the dinoflagellate Ceratium balechii

Oxygen deficiency in the southern Benguela has a pronounced negative impact on living marine resources and within the greater St Helena Bay anoxia is the cause of large episodic mortalities of the rock lobster Jasus lalandii. These impacts have motivated further investigation, specifically of the role of high biomass dinoflagellate blooms, commonly known as red tides, in the development of anoxic conditions. A high resolution time series of dissolved oxygen concentrations obtained from a bottom mooring off Elands Bay, located within the greater St Helena Bay region, is examined in relation to the development of an exceptional bloom of the dinoflagellate Ceratium balechii and an anoxia-induced mass mortality. A clear seasonal trend is evident in bottom dissolved oxygen concentrations, initiated in spring by upwelling events that advect low oxygen waters across the shelf. Increased deposition of organic carbon derived from primary production maxima in summer and autumn, together with the development of an increasingly stratified environment exacerbate dissolved oxygen deficits leading to a progressive decline in dissolved oxygen concentrations in the cold bottom layer. Within this seasonal timeframe episodic anoxia may occur throughout the water column of shallow inshore regions following the decay of red tides accumulated within these environments under conditions of persistent downwelling. Anoxia within these shallow non-stratified nearshore regions is dependent on exceptional organic loading of the water column as afforded by the decay of red tide and to the absence of wind-induced mixing or wave action. These requirements contribute to the local and transient character of these events of anoxia. With the onset of winter strong mixing results in reduced primary production and increased ventilation of bottom waters causing an increase in dissolved oxygen concentrations.

Evaluation of the water quality in the Guadarrama river at the section of Las Rozas‐Madrid, Spain

AbstractThe variation of the water quality of the Guadarrama river and its tributaries in a section of Las Rozas‐Madrid, Spain, was studied during the time period between January 2003 and January 2008. The parameter water quality index (WQI) was used to determine the water quality based on the conventional parameters of pollution. It was found that the WQI was slightly affected in the section evaluated. The value of the WQI was in the range of 56–64, which corresponded to the classification of ‘good quality’. It was determined that 64.3% of the organic matter present in the river was removed in the section of Las Rozas‐Madrid. The river acted as a plug flow reactor and a first‐order kinetics governed the ultimate biological oxygen demand (BOD5) (BODU) decay. The value of the first‐order constant demonstrated the river's high self‐purification capacity. In addition, a high linear relationship was found between the WQI and the dissolved oxygen deficit (D). Therefore, a quick determination of WQI may be carried out if the values of D are known. These are easily obtainable by field measurements.

Incorporation of oxygen contribution by plant roots into classical dissolved oxygen deficit model for a subsurface flow treatment wetland

It has been long established that plants play major roles in a treatment wetland. However, the role of plants has not been incorporated into wetland models. This study tries to incorporate wetland plants into a biochemical oxygen demand (BOD) model so that the relative contributions of the aerobic and anaerobic processes to meeting BOD can be quantitatively determined. The classical dissolved oxygen (DO) deficit model has been modified to simulate the DO curve for a field subsurface flow constructed wetland (SFCW) treating municipal wastewater. Sensitivities of model parameters have been analyzed. Based on the model it is predicted that in the SFCW under study about 64% BOD are degraded through aerobic routes and 36% is degraded anaerobically. While not exhaustive, this preliminary work should serve as a pointer for further research in wetland model development and to determine the values of some of the parameters used in the modified DO deficit and associated BOD model. It should be noted that nitrogen cycle and effects of temperature have not been addressed in these models for simplicity of model formulation. This paper should be read with this caveat in mind.

Simplified DO sag models for rapid BOD removal

Predictive models for dissolved oxygen deficit have been developed based on an exponential form of expression for the equivalent linear removal of the settleable component of biochemical oxygen demand. These models are more convenient to use than other models because they are applicable for any distance from the outfall and for point and non-point wastewater discharge conditions.

Water Quality Modeling and Dissolved Oxygen Balance in Streams: A Point Source Streeter‐Phelps Application in the Case of the Harsit Stream

AbstractThe Harsit Stream flowing into the Black Sea is an important watershed in the northeastern part of Turkey. The monthly averages of dissolved oxygen, carbonaceous biochemical oxygen demand, temperature, pH, total suspended solids, total phosphorus and total nitrogen were obtained for the water samples taken from the Tekke, Akcakale and Haciemin sites of the Harsit Stream. Water quality parameters were analyzed and evaluated according to the WHO standards and the Turkish Water Pollution Control Regulation. Initially, the variations in the dissolved oxygen profile were determined from dissolved oxygen, temperature and carbonaceous biochemical oxygen demand measurements by using the point source Streeter‐Phelps equation. Critical dissolved oxygen deficit values were calculated for the monthly average from January–December 2005, which are below the limit value (4 mg L–1) excluding April (7.26 mg L–1) and May (5.98 mg L–1) in the Harsit Stream, resulting in it having second class water quality in terms of dissolved oxygen concentration, temperature, pH and biochemical oxygen demand. It is also seen that the minimum dissolved oxygen limit value (8 mg L–1), which is a desired quantity for drinking water, is under the limit value for all months in the case of the water mixture. In particular, during the summer months, the consumption speed of oxygen is greater than the production speed of oxygen with increasing temperature and decreasing discharge, and negative values (anoxia) of dissolved oxygen sag are seen. These situations call for significant precautions and treatment criteria.

Effects of cooling water discharges from a power plant on reservoir water quality

Abstract The use of natural or artificial water reservoirs by thermal power plants for cooling purposes alterswater ecosystems. Water ecosystems are mainly subjected to the abiotic influences of higher temperature and increased mixing. This study presents the thermal and oxygen conditions in a lake used for cooling water as well as the chemical changes occurring in it. There is a spatial differentiation in the temperature of the water surface over time periods (in summer and winter). The vertical water temperature changes were definitely different from those of natural, unaffected lakes. Apart from a higher average water temperature, typical mixing and stratification periods were not observed. This apparently affected the dissolved oxygen conditions. The observed absence of a dissolved oxygen deficit resulted from the lack of a thermocline, which positively affected water quality. As a result, the two anthropogenic factors, i.e., the discharge of warm water and increased mixing, have flattened the negative effects on the lake. A new characteristic equilibrium for this lake was established. Single factors have been compensated for by this equilibrium. A relationship between temperature and biomass concentration was observed. The trophic state index (TSI) values permit classifying Rybnik Reservoir as a eutrophic lake.

Comparison of wetland and agriculture drainage as sources of biochemical oxygen demand to the San Joaquin River, California

For many years, the San Joaquin River (SJR) has had low dissolved oxygen conditions intermittently during the late summer and early fall. The low dissolved oxygen conditions are impacting critical fish habitat and the SJR is being regulated under a state of California remediation plan that includes the development of a total maximum daily load (TMDL) allocation for oxygen demanding substances. In support of the development of a scientific TMDL allocation, studies are being conducted to characterize water quality in the many tributaries of the SJR. This study identified the sources of biochemical oxygen demand (BOD) in two western tributaries of the SJR, Mud Slough and Salt Slough, and measured the loads of BOD, algae, and ammonia entering the SJR from wetland and agricultural sources. Mud and Salt Sloughs drain the Grassland Watershed. The watershed contains seasonal wetlands, irrigated farmland, and other agricultural lands. This drainage is under close regulatory scrutiny, because it produces a majority of the selenium and boron entering the SJR. In this study, wetland and irrigated agricultural drainage were sampled separately and a comparison was made to determine differences in water quality. In addition, water entering the study area was compared to water exiting the study area to determine the effect of water use in the region on water quality. This study demonstrated that BOD loads from the Grassland Watershed to the SJR were proportional to flow during June–October, the most critical time for dissolved oxygen deficits in the lower SJR. This indicates that Mud and Salt Sloughs are not producing more BOD than other tributaries in the region that are not under close regulatory scrutiny. The BOD concentration of wetland drainage is higher than that of agricultural drainage, but the higher agricultural drainage flows result in a higher mass loading of BOD. Wetland flooding and irrigation of crops both had a negative impact on water quality. Algal growth was identified as the major source of BOD in agricultural drainage and locations where BOD control could potentially be implemented were identified.

Physical background of the development of oxygen depletion in ice-covered lakes

The effect of the heat interaction between a water column and sediments on the formation, development, and duration of existence of anaerobic zones in ice-covered lakes is estimated based on observational data from five frozen lakes located in northwestern Russia and North America. A simple one-dimensional model that describes the formation and development of the dissolved oxygen deficit in shallow ice-covered lakes is suggested. The model reproduces the main features of dissolved oxygen dynamics during the ice-covered period; that is, the vertical structure, the thickness, and the rate of increase of the anaerobic zone in bottom layers. The model was verified against observational data. The results from the verification show that the model adequately describes the dissolved oxygen dynamics in winter. The consumption rates of DO by bacterial plankton and by bottom sediments, which depend on the heat transfer through the water-sediment interface, are calculated. The results obtained allow the appearance of potentially dangerous anaerobic zones in shallow lakes and in separate lake areas, which result from thermal regime changes, to be predicted.

Analysis of pollution status of Amadi Creek and its management

In this research work, the oxygen sag curve and purification capacity of Amadi Creek was studied. The reaeration constant ( k 2 ) was computed from data generated by sampling the DO concentration along the creek from the point of waste discharge downstream while the deoxygenation constant ( k 1 ) was determined by monitoring the BOD of samples obtained along the creek. The reaeration coefficient ranged from 0.09 d −1 to 0.17 d −1 . The Streeter–Phelps formula grossly under-estimated k 2 . Hence, a new empirical model was derived by multiple regression analysis and was successfully verified with an independent set of data. The study not only identified and quantified the amount of effluent into the creek from various sources but also evaluated its assimilatory capacity which is important information for the prevention of further degradation of the creek water. The critical dissolved oxygen deficit was 3.6 mg/l while the existing dissolved oxygen was also 3.6 mg/l which falls below the 5.0 mg/l stipulated for fish life. The high level of pollution in the creek calls for some critical implementation of the recommended strategies.

Use of the water quality index and dissolved oxygen deficit as simple indicators of watersheds pollution

Abstract The use of the water quality index (WQI) and the dissolved oxygen deficit (D) as simple indicators of the watersheds pollution was investigated and compared in the Municipality of Las Rozas (north-west of Madrid, Spain). The quality of the water in Guadarrama and Manzanares rivers and Paris Park ponds, the main watersheds of this area was investigated during 2 years (from September 2001 to September 2003). It was found that the WQI was very useful for the classification of the waters monitored. The WQI was 70, which corresponds to “good” quality water at the sampling point 1 (entrance of Las Rozas) and decreased to around 64 (medium quality) at the sampling point 6 (outlet of Las Rozas) in the case of Guadarrama River. The WQI was around 65 in the influents of Manzanares River. Finally, in Paris Park the WQI ranged from around 72–55, which corresponded to a classification from “good” to “medium” quality, respectively. A high linear relationship between the WQI and the dissolved oxygen deficit (D) was found. Therefore, a fast determination of WQI may be carried out knowing the values of D, which are easily obtainable by field measurements. It was found an influence of the climate conditions on the values of WQI and D.

English

The Stockton Deep Water Ship Channel, a stretch of the tidal San Joaquin River, is frequently subject to low dissolved oxygen conditions and annually violates regional water quality objectives. Underlying mechanisms are examined here using the long-term water quality data, and the efficacy of possible solutions using time-series regression models. Hypoxia is most common during June-September, immediately downstream of where the river enters the Ship Channel. At the annual scale, ammonium loading from the Regional Wastewater Control Facility has the largest identifiable effect on year-to-year variability. The longer-term upward trend in ammonium loads, which have been increasing over 10% per year, also corresponds to a longer-term downward trend in dissolved oxygen during summer. At the monthly scale, river flow, loading of wastewater ammonium and river phytoplankton, Ship Channel temperature, and Ship Channel phytoplankton are all significant in determining hypoxia. Over the recent historical range (1983–2003), wastewater ammonium and river phytoplankton have played a similar role in the monthly variability of the dissolved oxygen deficit, but river discharge has the strongest effect. Model scenarios imply that control of either river phytoplankton or wastewater ammonium load alone would be insufficient to eliminate hypoxia. Both must be strongly reduced, or reduction of one must be combined with increases in net discharge to the Ship Channel. Model scenarios imply that preventing discharge down Old River with a barrier markedly reduces hypoxia in the Ship Channel. With the Old River barrier in place, unimpaired or full natural flow at Vernalis would have led to about the same frequency of hypoxia that has occurred with actual flows since the early 1980s.

A biogeochemical model for metabolism and nutrient cycling in a Southeastern Piedmont impoundment

While non-point nutrient loads are important determinants of biological productivity in Southeastern Piedmont impoundments, productivity can be attenuated by concomitant sediment loads that reduce the biological availability of these nutrients. A biogeochemical model is proposed that explicitly accounts for the effects of sediment–nutrient interactions on multiple components of phytoplankton metabolism dynamics, including algal photosynthesis and respiration, pH, carbonate speciation, dissolved oxygen, and biochemical oxygen demand. Sediment–nutrient interactions relate nutrient uptake and release to pH, sediment oxygen demand, sediment organic matter, and iron. pH is a state variable in our model, affects sediment–nutrient adsorption, and constrains model parameters. The model replicates water quality observations in a small Southeastern Piedmont impoundment and suggests that pH-dependent sediment–nutrient adsorption dominates both orthophosphate and ammonium dynamics, with phosphate adsorption being controlled by ligand exchange to iron oxides, and ammonium adsorption being controlled by the cation exchange capacity. Sediment organic matter accumulation and decay also affects nutrient availability, and may explain the long-term increase of hypolimnetic dissolved oxygen deficit in Lake Lanier, a large Southeastern Piedmont impoundment.