Sediment Oxygen Demand Values Research Articles

Effects of Diel Oxygen Cycling and Benthic Macrofauna on Sediment Oxygen Demand

This field study examined how sediment macroinfauna change patterns of sediment oxygen demand (SOD) throughout a diel oxygen cycle. Sediments with a greater faunal presence would be expected to have greater overall SOD, and at night may alter their behavior and influence SOD depending on their response to low-oxygen stress. Dynamic faunal bioturbation or bioirrigation behavior would also result in corresponding variation in SOD values on short time scales. In situ flow-through benthic metabolism chambers were used to measure SOD at a high temporal resolution in discrete sediment patches. Sediments with more macroinfauna had greater average SOD over the diel cycle, consistent with previous studies. Where more macroinfauna were present, they drove greater SOD during nightly low oxygen, presumably by enhancing their burrowing and irrigation activities. SOD was also more variable on a sub-diel timescale in sediments with more macroinfauna. Sediment oxygen demand is dynamic and highly sensitive both temporally, on very short timescales, and spatially, in terms of resident fauna, and their interaction produces heretofore unaccounted complexity in patterns of SOD particularly in shallow coastal systems. Extrapolations of temporally and spatially limited SOD measurements to a system-wide scale that do not account for the short-term and spatially variable effects of fauna may produce imprecise and misleading estimates of this critical ecosystem function.

A sediment diagenesis model on sediment oxygen demand in managing eutrophication on Taihu, China.

Blue-green algae (CyanoHABs), photosynthetic bacteria that create a harmful aquatic environment, have been a trending issue on Taihu for over a decade. CyanoHABs adapt to varying climatic changes, which explains why the problem on Taihu still thrives. One major drive that keeps the algae is Sediment Oxygen Demand (SOD). In this paper, seasonal and spatial variations of SOD that contribute immensely to nutrient growth in Lake Taihu were done using the Environmental Fluid Dynamics Code (EFDC). The results were analyzed based on Nitrogenous SOD (NSOD) and Total SOD (TSOD). Summer results ranged from - 0.05754 to - 0.0826 (- 0.75658 to - 0.83902) (g/m2/day) and Winter values ranged from - 0.3022 to - 0.40171 (- 1.34486 to - 1.48856) (g/m2/day) indicate a gradual decrease in NSOD (TSOD) values respectively. Relatively higher values in summer are attributed to warmer surface water which sets up thermal stratification to increase the internal loading of nitrogen. Lower winter values are related to inverse stratification, where lower oxygen concentration decreases the SOD to trigger ammonium accumulation in the water column. NSOD (TSOD) values for Autumn results ranged from - 0.1039 to - 0.24786 (- 0.96251 to - 1.39454) (g/m2/day) and Spring values of - 0.43019 to - 0.35959 (- 1.48297 to - 0.54089) (g/m2/day). Transition seasons (i.e., Autumn and Spring) results are impacted by wind mixing that allows dissolved oxygen and nutrients in the whole water column. However, spring values depict a gradual increase in SOD value attributed to spring turnover and gradual stratification, which decrease nutrient concentration. In contrast, decreasing SOD values in autumn are related to mixing, but temperature decreases tend to increase nutrient concentrations. Carbonaceous sediment oxygen demand (CSOD), due to sulfide oxidation, presents high values from the difference between TSOD and NSOD. Based on the high values of CSOD, it is highly recommended that more research on eutrophic Taihu lakes would consider delving into CSOD.

Empirical modeling of hypolimnion and sediment oxygen demand in temperate Canadian lakes

ABSTRACT Sediment oxygen demand (SOD) and hypolimnetic oxygen demand (HOD) drive deep-water dissolved oxygen (DO) depletion in lakes, yet these parameters can be difficult to be measure routinely. To address this issue, we present an empirical DO depletion model from time-series measurements of hypolimnetic DO and water-column temperature profiles to estimate hypolimnion thickness (H). The model is based on a dataset that includes 3 temperate lakes (Lake Erie, Lake Simcoe, and Eagle Lake) in Ontario, Canada, of varying size and trophic state. We report SOD (mean [standard deviation]; 0.30 [0.07] g m−2 d−1) and HOD (0.08 [0.03] g m−3 d−1) values based on regression fits of (where t is time) and H from these lakes. The model shows that when vertical (through thermocline) and horizontal fluxes can be neglected in the DO budget during summer, SOD and HOD are the first-order parameters driving . The empirical model predicted hypolimnetic DO in the 3 lakes (root-mean-square error [RMSE] of DO < 3.58 g m−3) and was subsequently validated against observations from a fourth lake (Little Silver Lake, Ontario; RMSE of DO = 1.07 g m−3). The model provides insight into the importance of physical characteristics (i.e., 1/H) in the hypolimnetic DO budget and the relative impact of physical transport versus biogeochemical sources and sinks in the DO budget. When the spring turnover DO concentration is known, the model can be used to simulate depletion of DO in the hypolimnion, including the onset of hypoxia, using routinely collected temperature profile data. We suggest that the proposed values for SOD and HOD can serve as estimates for water quality model calibration when no information is available.

Sediment Oxygen Demand: A Review of In Situ Methods

Sediment oxygen demand (SOD) plays a fundamental role in biological and chemical processes within the benthic layer of a water body. Land use, including agricultural land use, can affect SOD. However, a wide variety of approaches have been used for in situ SOD chamber construction and data collection, and modelers frequently use SOD values from the literature, without consideration of the differences in methods. Here, we review existing literature on SOD chambers (32 papers, 1974-2016), compare the differences between in situ and laboratory methods, evaluate the effects of in situ chamber mixing, and discuss common challenges associated with deployment. A cohesive in situ sealed chamber design for use with a multiparameter water-quality instrument is presented as an effort toward standardizing SOD methodology, an important consideration that may facilitate integration of SOD data sets among multiple research efforts.

Study of the Relation between Sediment Characteristics and Multiphase Flow to the Presence of Sediment Oxygen Demand (SOD) in Open Channels

A laboratory study was conducted with the aim to determine the correlation between sediment characteristics and multiphase flow analysis of carrier fluid to the presence of SOD. Six sediment samples were tested on their physical and chemical characteristics along with particle size distribution of sediments to find the indication of oxygen consumption and to classify the soil sediment class. For multiphase flow analysis, there were two transition velocities calculated: the transition between a pseudo-homogenous flow and a heterogeneous flow and the limit deposit velocities at the onset of solid particle bed. The SOD test was done in laboratory-scale by using a 600-mL reactor. According to tests, the amount of organic carbon content (TOC) in the samples were ranging from 34.58 to 81.27%, with the sediments’ textures categorised as silt loam, silty clay loam, and sand. In the channels, heterogeneous flow occurred in two channel segments, while the other segments’ regime was classified as homogeneous flow. The obtained SOD values were varied from 0.2427 to 0.8487 g/m2/day with K3 values obtained ranged from 8.6537 to 12.4028 m-1. Based on all analysis, the organic characteristic of sediment holds a key role in the presence of SOD value.

Potential linkage between sediment oxygen demand and pore water chemistry in weir-impounded rivers

Due to recent weir construction on four major rivers in South Korea, sediment has accumulated in the river bottom near the weirs, which has in turn raised concerns over the quality of overlying water. In this study, the seasonal and spatial variations of sediment oxygen demand (SOD) and the influencing factors were explored using pore water chemistry for the weir-impounded rivers. Muddy and sandy sediment samples were taken from 24 different sites along the four major rivers in summer and autumn, 2016. The SOD was measured in a laboratory based on 10-hour incubation at in situ temperature. The measured pore water chemistry included the concentrations of dissolved organic carbon (DOC), total dissolved nitrogen (TDN), inorganic nitrogen (NH3-N, NO3-N, NO2-N), and phosphate phosphorous (PO4-P), and the optical properties from UV absorption spectra and fluorescence excitation-emission matrixes coupled with parallel factor analysis (EEM-PARAFAC). Significant differences in SOD values between muddy and sandy sediments were found only in summer (p=0.047). The higher SOD in summer versus autumn (p=0.015) was attributed to seasonal temperature differences. The higher NH3-N and the lower NO3-N of the pore water samples in summer versus autumn suggested that organic nitrogen decomposition via an ammonification and nitrification process could operate as an important factor for the SOD variations in summer and autumn, respectively. Principal component analysis revealed the mutual contributions of nitrogen-associated processes and the organic composition in pore water to increasing SOD levels. NH3-N in sediment pore water alone could be a good predictor for SOD. However, multiple regression analysis using NH3-N, fluorescence index and terrestrial humic-like components improved the estimation capability for SOD variations.

Organic matter remineralization in marine sediments: A Pan‐Arctic synthesis

AbstractClimate change in the Arctic is ongoing and causes drastic modification on the ecosystem functioning. In soft‐bottom environments, organic matter remineralization is considered an important ecosystem function. Here we provide a large‐scale assessment of the current knowledge on the benthic organic matter remineralization and its potential response to climate change. Sediment oxygen demand (SOD) values (n = 1154), measured throughout the Arctic, were gathered from 30 publications and 16 databases, and nutrient flux values, available in a far lesser extent (n &lt; 80), were also compiled. Generalized additive models were used to estimate the influence of explanatory variables on benthic oxygen fluxes and for interpolating SOD to the whole Arctic region. This first Pan‐Arctic review of the distributions of SOD showed that oxygen fluxes strongly depended on water depth, i.e., followed the general trend observed for other regions, and also on the availability of labile organic matter. The continental shelves (representing ~50% of Arctic Ocean's total area) were characterized by the highest SOD values (10.5 ± 7.9 mmol O2 m−2 d−1), and differences among shelves were observed; SOD values in inflow, interior, and outflow shelves were 11.8 ± 8.0, 6.2 ± 5.6, and 3.9 ± 3.5 mmol O2 m−2 d−1, respectively. Moreover, seasonal variation in SOD changed significantly among areas. The interpolation based on the best fitted model showed high respiration in the inflow and interior shelves. In the inflow shelves, characterized by productive waters, benthic activities replenish bottom water with nutrients which may augment primary productivity, whereas sediments from the interior shelves, e.g., under the direct influence of the Mackenzie River, consume nutrients.

Determination of Sediment Oxygen Demand in the Ziya River Watershed, China: Based on Laboratory Core Incubation and Microelectrode Measurements.

A study coupling sedimentcore incubation and microelectrode measurementwas performed to explore the sediment oxygen demand (SOD) at 16 stations in the Ziya River Watershed, a severely polluted and anoxic river system in the north of China. Total oxygen flux values in the range 0.19–1.41 g/(m2·d) with an average of 0.62 g/(m2·d) were obtained by core incubations, and diffusive oxygen flux values in the range 0.15–1.38 g/(m2·d) with an average of 0.51 g/(m2·d) were determined by microelectrodes. Total oxygen flux obviously correlated with diffusive oxygen flux (R2 = 0.842). The microelectrode method produced smaller results than the incubation method in 15 of 16 sites, and the diffusive oxygen flux was smaller than the total oxygen flux. Although the two sets of SOD values had significant difference accepted by the two methods via the Wilcoxon signed-rank test (p < 0.05), the microelectrode method was shown to produce results that were similar to those from the core incubation method. The microelectrode method, therefore, could be used as an alternative method for traditional core incubation method, or as a method to verify SOD rates measured by other methods. We consider that high potential sediment oxygen demand would occur in the Ziya River Watershed when the dissolved oxygen (DO) recovered in the overlying water.

Dissolved Oxygen Dynamics at the Sediment–Water Column Interface in an Urbanized Stream

This manuscript reports findings on sediment oxygen demand (SOD), gross primary production (GPP), net daily metabolism (NDM), and stream reaeration in an urbanized stream, the Jordan River, in Utah. The river has two segments; the Lower Jordan River, which is impaired for dissolved oxygen (DO) and the Upper Jordan River, which is fast flowing with coarse sediments and has no DO impairment. Summer SOD values for the Lower Jordan River ranged from a high 2.2 g DO/m2 per day to a low of 0.97 g DO/m2 per day with most of the sampled sites in the Lower Jordan River having SOD values greater than 1 g DO/m2 per day. SOD values correlated well with volatile solids in surface sediments of the Lower Jordan River. The Upper Jordan River showed SOD values as high as 3.0 g DO/m2 per day, which was attributed to hyporheic exchanges or groundwater upwelling. All sampled sites exhibited high SOD values in winter. A modified chamber method was employed to estimate community respiration (CR24), GPP, and NDM, while characterizing both the water column and benthos. In summer 2010, the sediment tray primary production (TPP) ranged from 1.0 to 7.4 g DO/m2 per day. In winter 2011, TPP ranged from 0.7 g DO/m2 per day to a high value of 5.6 g DO/m2 per day. NDM values indicated that the Upper Jordan River is a year round source of in-stream produced organic matter to the downstream Lower Jordan River with the majority of organic matter produced in the benthos. Reaeration measurements showed that the potential for reaeration is much higher in the mid-sections of the Jordan River, where the river has increased flow velocities due to topography, decreased depths, and a less uniform bottom.

Model development for prediction and mitigation of dissolved oxygen sags in the Athabasca River, Canada

Northern rivers exposed to high biochemical oxygen demand (BOD) loads are prone to dissolved oxygen (DO) sags in winter due to re-aeration occurring within limited open water leads. Additionally, photosynthesis is reduced by decreased daylight hours, inability of solar radiation to pass through ice, and slower algal growth in winter. The low volumetric flow decreases point-source dilution while their travel time increases. The Athabasca River in Alberta, Canada, has experienced these sags which may affect the aquatic ecosystem. A water quality model for an 800km reach of this river was customized, calibrated, and validated specifically for DO and the factors that determine its concentration. After validation, the model was used to assess the assimilative capacity of the river and mitigation measures that could be deployed. The model reproduced the surface elevation and water temperature for the seven years simulated with mean absolute errors of <15cm and <0.9°C respectively. The ice cover was adequately predicted for all seven winters, and the simulation of nutrients and phytoplankton primary productivity were satisfactory. The DO concentration was very sensitive to the sediment oxygen demand (SOD), which represented about 50% of the DO sink in winter. The DO calibration was improved by implementing an annual SOD based on the BOD load. The model was used to estimate the capacity of the river to assimilate BOD loads in order to maintain a DO concentration of 7mg/L, which represents the chronic provincial guideline plus a buffer of 0.5mg/L. The results revealed the maximum assimilative BOD load of 8.9ton/day at average flow conditions, which is lower than the maximum permitted load. In addition, the model predicted a minimum assimilative flow of about 52m3/s at average BOD load. Climate change scenarios could increase the frequency of this low flow. A three-level warning-system is proposed to manage the BOD load proactively at different river discharges. Other mitigation options were explored such as upgrading the wastewater treatment of the major BOD point source and oxygen injection in the effluents. The model can be used as a management tool with updated SOD values to forecast the DO in low flow years and evaluate mitigation measures. As well, the methodology presented here can be applied to manage other ice-covered rivers.

Measurement of sediment oxygen demand for modeling the dissolved oxygen distribution in a Subalpine lake

Sediment oxygen demand (SOD) is believed to be an important process affecting dissolved oxygen (DO) concentrations and has become an integral part of modeling dissolved oxygen (DO) in surface water bodies. Because no SOD data are measured at specific study sites, it is common for researchers to take SOD values from the literature for use in DO modeling. This paper focuses on an approach for measuring sediment oxygen demand in the laboratory using undisturbed sediment core samples in the Yuan-Yang Lake (YYL) of north-central Taiwan. The measured SOD values among six sampling stations were within the range of 0.06 to 4.50 g/m2/day at a temperature of 20°C. The ordinary kriging method was then applied to map the spatial distribution of the monthly average SOD values, which were incorporated into a three-dimensional water quality model for simulating the dissolved oxygen distribution of the lake. The simulation results accurately reflect the field-measured DO concentrations. Model sensitivity analyses were also conducted with increasing and decreasing 30% SOD values based on the monthly average SOD in the spatial distribution. The simulated results reveal that SOD had a significant impact on the DO concentrations in the lake. The present work, with its field measurements and numerical modeling, will provide assistance in lake water quality management. Key words: Sediment oxygen demand, dissolved oxygen, measurement, water quality model, kriging, Yuan-Yang Lake.

Monitoring sediment oxygen demand for assessment of dissolved oxygen distribution in river

Sediment oxygen demand (SOD) has become an integral part of modeling dissolved oxygen (DO) within surface water bodies. Because very few data on SOD are available, it is common for modeler to take SOD values from literature for use within DO models. SOD is such an important parameter in modeling DO that this approach may lead to erroneous results. This paper reported on developing an approach for monitoring sediment oxygen demand conducted with undisturbed sediment core samples, where the measured results were incorporated into a water quality model for simulating and assessing dissolved oxygen distribution in the Xindian River of northern Taiwan. The measured results indicate that a higher freshwater discharge results in a lower SOD. Throughout a 1-year observation in 2004, the measured SOD ranged from 0.367 to 1.246 g/m(2)/day at the temperature of 20°C. The mean values of the measured SOD at each station were adopted in a vertical two-dimensional water quality model to simulate the DO distribution along the Xindian River. The simulating results accurately depict the field-measured DO distribution during the low and high flow conditions. Model sensitivity analyses were also conducted with increasing and decreasing SOD values for the low and high flow conditions and revealed that SOD had a significant impact on the DO distribution along the Xindian River. The present work combined with field measurements and numerical simulation should assist in river water quality management.

High Sediment Oxygen Demand Within an Instream Swamp in Southern Georgia: Implications for Low Dissolved Oxygen Levels in Coastal Blackwater Streams1

Todd, M. Jason, George Vellidis, R. Richard Lowrance, and Catherine M. Pringle, 2009. High Sediment Oxygen Demand Within an Instream Swamp in Southern Georgia: Implications for Low Dissolved Oxygen Levels in Coastal Blackwater Streams. Journal of the American Water Resources Association (JAWRA) 45(6):1493‐1507.Abstract: Sediment oxygen demand (SOD) is considered a critical and dominant sink for dissolved oxygen (DO) in many river systems including blackwater streams and is often poorly investigated or roughly estimated in oxygen budgets. The purposes of this study are to (1) characterize and document the magnitude and variability of SOD in representative instream swamps found on the Georgia Coastal Plain; (2) predict SOD from more readily measured parameters such as soil, sediment, and litter organic carbon; and (3) obtain an accurate representation of SOD values within this understudied habitat to help improve water quality models and the continued development of DO as an appropriate water quality standard. Results show SOD rates ranging from 0.491 to 14.189 g O2/m2/day, up to 18 times higher than values reported for southeastern sandy‐bottomed streams and suggest that instream swamps are repositories of large amounts of organic matter and are thus areas of intense oxygen demand and a major factor in determining the oxygen balance of the watershed as a whole. These areas of intense oxygen demand in relatively unimpacted areas indicate that low DO concentrations may be a natural phenomenon. SOD rates were significantly correlated (alpha = 0.05) with a number of sediment parameters, with organic carbon and total organic carbon being the best predictors of SOD rate. When developing water quality models, managers should pay closer attention to the influence of SOD as it plays a critical role in determining DO levels within instream swamps and the river system.

Sediment Oxygen Demand and Nutrient Fluxes for a Tropical Reservoir in Singapore

Sediment oxygen demand (SOD) and nutrient flux studies were conducted for a tropical reservoir in Singapore in order to determine the approximate SOD and nutrient release rates from the sediments. SOD values obtained from laboratory experiments ranged from 1.4 to 3.3 g O2 / m2 -day . Similar results were also obtained by calculating SOD values from in situ DO measurements taken in the field. The nutrient flux study was performed in the laboratory at a constant temperature of 25°C in oxic and anoxic columns. Except for nitrate+nitrite , higher nutrient release rates were generally observed under anoxic conditions. The ammonium release rate was 0.06 g O2 / m2 -day under oxic conditions and 0.117 g O2 / m2 -day under anoxic conditions. The nitrate flux rate was 0.17 g O2 / m2 -day under oxic conditions but was negligible under anoxic conditions. Orthophosphate flux results were negative throughout the oxic incubation implying that sediments acted as a sink. The release rate of orthophosphate was 0.007 6 ...

Measurement of sediment oxygen demand for modelling dissolved oxygen distribution in tidal Keelung River

AbstractThe Keelung River is one of the major branches of the Danshuei River estuarine system, which runs the metropolitan capital city of Taipei, Taiwan, and receives a large of amount of wastewater. The dissolved oxygen (DO) concentration is generally low in the tidal portion of the Keelung River. Hypoxia/anoxia occurs often, particularly during a low‐flow period. The sediment oxygen demand (SOD) amounts to a significant value, hence increasing the total oxygen demand load of the river. The present work reports on laboratory SOD made on grab sediment core samples in situ that are undisturbed. The results reveal that SOD values fluctuate with variations in seasons and are higher in summer due to a high‐temperature effect. It was found in the laboratory tests that the average SOD (at 20 °C) value is 0.76 g/m2/day and the maximum SOD (at 20 °C) value reaches 1.58 g/m2/day. The mean values of measured SOD at each station were adopted in the vertical two‐dimensional water quality model to simulate the DO distribution along the tidal Keelung River. The simulated results are in reasonable agreement with the measured DO distribution in the river. Model sensitivity analyses were also conducted with increasing and decreasing SOD. It reveals that SOD is an important parameter that affects the DO distribution in the tidal estuary.

Factors Affecting Sediment Oxygen Demand Dynamics in Blackwater Streams of Georgia’s Coastal Plain1

Abstract: Sediment oxygen demand (SOD) is believed to be an important process affecting dissolved oxygen (DO) concentrations in blackwater streams of the southeastern coastal plain. Because very few data on SOD are available, it is common for modelers to take SOD values from the literature for use with DO models. In this study, SOD was measured in seven blackwater streams of the Suwannee River Basin within the Georgia coastal plain for between August 2004 and April 2005. SOD was measured using four in situ chambers and was found to vary on average between 0.1 and 2.3 g O2/m/day across the seven study sites throughout the study period. SOD was found to vary significantly between the watersheds within the Suwannee River Basin. However, land use was not found to be the driving force behind SOD values. Statistical analyses did find significant interaction between land use and watersheds suggesting that an intrinsically different factor in each of the watersheds may be affecting SOD and the low DO concentrations. Further research is needed to identify the factors driving SOD dynamics in the blackwater streams of Georgia’s coastal plain. Results from this study will be used by the Georgia Department of Natural Resources – Environmental Protection Division as model input data for the development and evaluation of DO total maximum daily loads in the Georgia coastal plain.

Application and Validation of the Spreadsheet Method for Determining SOD

The justification and conceptualization of the measure-plus-calculate method for measuring sediment oxygen demand (SOD) without the use of a benthic chamber are described in a companion article. The spreadsheet-based steady-state and transient solutions to the sediment oxygen consumption and transport equations used to determine SOD are also developed and discussed in the companion article. This article discusses parameter determination for, and validation of, the measure-plus-calculate technique. The SOD determinations from this method are compared to those made at the same site using in situ benthic chambers in the Arroyo Colorado River. The SOD determination model is modified to account for both forced convection equations describing the free-stream condition and natural convection equations describing the condition of isolated water within a benthic chamber. Linear regression is used to compare chamber-measured SOD to that determined using the proposed technique and indicates good agreement. Correlation coefficients are 0.93 for the steady-state model and 0.91 for the transient model. Predictions of free-stream SOD simulating natural conditions in the absence of chambers are greater than chamber-measured SOD values. Model predictions of SOD as a function of stream velocity, temperature, and DO are shown and discussed. The proposed technique shows potential for use as a method for determining SOD, but further study is necessary to confirm this in a wide variety of water systems.

Impacts of water depth, sediment pigment concentration, and benthic macrofaunal biomass on sediment oxygen demand in the western Arctic Ocean

We investigated the impacts of water depth, sediment pigment concentration, and benthic macrofaunal biomass on sediment oxygen demand (SOD) during three cruises to the western Arctic Ocean. SOD values were similar to those of most studies from the Arctic and ranged from a high of 20.68 mmol O2·m–2·day–1 at a shallow shelf station to a low of 0.29 mmol O2·m–2·day–1 at the deepest basin station (3648 m). SOD was significantly greater at shallow sites (&lt;500 m; mean = 7.39 mmol O2·m–2·day–1; standard deviation (SD) = ±5.38) than at deep sites (&gt;500 m; mean = 1.39 mmol O2·m–2·day–1; SD = ±0.96). As hypothesized, SOD was negatively correlated with water depth and positively correlated with both surface-sediment pigment concentration and macrofaunal biomass, with macrofaunal biomass explaining approximately 74% of the variability in SOD. We propose that higher macrofauna-normalized respiration rates (i.e., SOD divided by macrofaunal biomass) in deep water indicate that microbial–meiofaunal respiration predominates in deep versus shallow water. Finally, deeper stations associated with Barrow Canyon had SODs, benthic macrofaunal biomass, and surface-sediment pigment concentrations that were similar to those of shallower shelf locations, suggesting down-canyon transport of organic material.

Water Quality in the Integrated Mariculture Pond Systems (IMPS) at Makoba Bay, Zanzibar, Tanzania

Keywords: water quality, nutrients, dissolved oxygen, pH, half life, rate constants, sediment oxygen demand, integrated mariculture, Chanos chanos The Makoba integrated mariculture pond system project (IMPS) has been on-going since 1998. Except for a period from mid 1999 to 2001, various water quality parameters, namely temperature, salinity, pH, dissolved inorganic nutrients and dissolved oxygen concentration and saturation, have been monitored continuously. In 2002, measurement of sediment oxygen demand (SOD) and consumption of oxygen by sediments was initiated. Dissolved oxygen concentration varied from the highest monthly average of 7.16 mg/l in October 1998, to 2.2 mg/l in March 2000 (r = –0.69). Nutrient concentrations remained moreor- less constant, except in the finfish ponds, where slight variations were recorded. The lowest concentration of ammonium-nitrogen (3.02 mg-at N/l) was recorded in the Kiwani creek in December 2001, and the highest (18.02 mg-at N/l), in the finfish ponds in December 1998. In 2002 the concentrations became much lower and the overall regression from 1998 to 2002 was negative. Dissolved inorganic phosphate concentration in the finfish ponds increased from 4.36 to 7.97 mg-at P/l (r = 0.75) between August 1998 and April 1999. In 2002, however, the concentration was low, making the overall trend also negative. pH ranged from 7.07 in Kiwani creek to 8.54 in the outlet. There was no clear pattern in the pH trends at the individual stations. In 1998 and 1999 there was a general decrease in pH with a corresponding increase in nutrient concentrations and decrease in dissolved oxygen. The SOD values in the ponds and the outlet were higher than in the creek and the reservoir, and the half life of dissolved oxygen was lowest in the ponds compared to the rest of the sites. The nutrient concentrations at Makoba ponds are generally acceptable for the environment and fish farming. Western Indian Ocean Journal of Marine Science Vol.2(1) 2003: 15-24

Quality of the Bottom Sediment Prior to Dredging in the Golden Horn of Istanbul

The Golden Horn has experienced severe pollution due to uncontrolled domestic and industrial wastewater discharges until recent years. A restoration project has been developed by our universities, upon a request from Istanbul Metropolitan Municipality. Two principal alternatives for the dredging and disposal of the bottom sediments were considered: disposing on the land and disposing in the sea. Both of these alternatives include several sub-alternatives. Characterization of the sediment quality is crucially important for selecting the best alternative considering the cost, environmental impact and public acceptance. However, only a few and rather old studies were present with which it was not possible to get a comprehensive information on the critical sediment characteristics. Therefore, the aim of this study was determination of spatial distribution of sediment characteristics. The project area, at which the sediment quality determined, covers the part of the Golden Horn remaining at the upstream of Valide Sultan Bridge. The number of sampling stations were thirteen and the sediment samples were collected from 0.0 m, 5.0 m and 10.0 m from the bottom surface. The following parameters were measured on each sample: Total solids, organic matter, total phosphorus, TKN, oil and grease, total sulphur, and sediment oxygen demand (SOD). Sediment oxygen demand parameter was further divided into three fractions, namely, biological (SOD-B) and chemical (SOD-C). Average organic content of the bottom sediment was around 10% while ammonia and sulfur exhibit very high levels. It is found that the bottom sediment is well stabilized with very low organic content below 5.0 m from the bottom surface. It can be said that, removing the upper 5 m of the bottom sediment will be enough for creating a relatively stable bottom surface which will cause oxygen depletion in the overlaying water at acceptable levels. High SOD values of the bottom sediment makes the alternatives considering disposal in the Marmara Sea and Black Sea inapplicable. High SOD-C values, especially, indicate that the sediment will cause a tremendous reduction in the oxygen concentration in a very short time at any marine environment, and even it may create anaerobic conditions. Therefore, disposal of dredged sediment into abandoned mines 4 km from the Golden Horn by a pressure pipeline has been chosen as the best applicable alternative.