Sediment Oxygen Demand Research Articles

Impact of Salinity Change on Water Quality Variables from the Sediment of an Artificial Lake under Anaerobic Conditions

Artificial reservoirs are created by dike construction in coastal areas to secure the agricultural water supply on the west coast of South Korea. These systems are found to retain brackish characteristics until total desalination is achieved. To evaluate the effects of salinity on the organic substances released from the sediment, a laboratory water-sediment column experiment was conducted to assess associated changes in water quality variables such as the sediment oxygen demand (SOD), chemical oxygen demand (COD), and concentrations of nitrogen (N) and phosphorus (P). Under high salinity conditions, the release of N from the sediment was promoted with the enhancement of SOD and COD. This trend was accounted for by the response of the microorganisms (cell breakdown of algae and suppression of metabolic activity). Our results suggest that chemicals (N, P, and COD) released from sediment and its overall impact on the water quality of a brackish lake should vary depending on the temporal and spatial dynamics of the salinity.

New Baseline for Understanding Arctic Oxygen and Nutrient Fluxes

Significant spatial and temporal patterns emerge from the first pan-Arctic comparison of oxygen demand in marine sediments.

Deepwater dynamics and mixing processes during a major inflow event in the central Baltic Sea

AbstractIntrusions of large amounts of dense and oxygen‐rich waters during so‐called Major Baltic Inflows (MBIs) form an essential component of the Baltic Sea overturning circulation and deepwater ventilation. Despite their importance, however, detailed observations of the processes occurring in the central basins during an MBI are virtually lacking. Here data from a long‐term deployment of an autonomous profiling platform located in the center of one of the main basins are presented, providing the first direct and detailed view of the deepwater modifications and dynamics induced by one of the largest MBIs ever recorded (MBI 2014/2015). Approximately, 21 Gmol of oxygen were imported during three distinct inflow phases with an unexpectedly large contribution of oxic intrusions at intermediate depth. Oxygen consumption rates during the stagnation period immediately following the inflow phase was found to be 87 g m−2 yr−1 with a dominant contribution of sedimentary oxygen demand. The most energetic deepwater processes (topographic and near‐inertial waves) were only marginally affected by the inflow; however, subinertial energy levels associated with intrusions and eddies were strongly enhanced. Turbulence microstructure data revealed that the deep interior regions remain essentially nonturbulent even during the energetic conditions of an MBI, emphasizing the importance of boundary mixing. Warm intrusions frequently showed a temperature fine structure with vertical scales of the order of 0.1 m, without any signs of active turbulence. At the upper flanks of these intrusions, double‐diffusive staircases were often found to develop, suggesting an important alternative mixing process during inflow conditions.

Influence of Crude Oil on Denitrification in Subtidal Sediments in the Northern Gulf of Mexico

In this study the impact of hydrocarbons on nitrogen cycling in intertidal sediments from a barrier island in the north central Gulf of Mexico was investigated. Initial total petroleum hydrocarbon (TPH) concentrations of the sediments averaged 49 ± 27 mg kg−1 in June and 75 ± 48 mg kg−1 in November. Following the addition of crude oil, TPH concentrations increased to 340 ± 73 and 296 ± 50 mg kg−1 in June and November, respectively. Sediment oxygen demand (SOD), inorganic nitrogen and phosphorus fluxes, and denitrification capacity, measured with the isotope pairing technique (IPT) within a week of oiling, were consistently higher in June compared to rates in November when temperatures were 10°C lower. Despite significantly higher TPH concentrations in the oiled treatments, SOD, nutrient fluxes, nitrogen fixation, denitrification, and anammox, did not differ between the treatments. Potential denitrification rates, measured in the presence of excess nitrate (100 μM), were similar between the control and oil treatments, but significantly higher than rates measured with the IPT. The elevated rates of potential denitrification suggest the presence of an active extant microbial community capable of significant attenuation of porewater nitrate concentrations. The insignificant changes in nitrogen cycling in response to petroleum hydrocarbon additions at a site with hydrocarbons present, albeit at low concentrations, suggests resiliency in nitrogen cycling in response to additional hydrocarbon inputs in ranges investigated in this study.

Effect of Temperature on Oxygen Profiles and Denitrification Rates in Freshwater Sediments

Vegetated ditches and wetlands are important sites for nutrient removal in agricultural catchments. About half of the influx of inorganic nitrogen can be removed from these ecosystems by denitrification. Previous studies have shown that denitrification in aquatic ecosystems is strongly temperature dependent, resulting from temperature-dependent oxygen availability. Here, we study short-term temperature effects on sediment oxygen demand (SOD) and the maximum depth of oxygen penetration into the sediment (Z), in relation to overall denitrification rates. We set up sixteen wetland microcosms at four different temperatures (11–25 °C), in which we determined SOD and Z from sediment oxygen microprofiles. Denitrification rates were measured using 15N-labeling, analysed by membrane inlet mass spectrometry. Temperature strongly affected sediment oxygen dynamics. SOD exponentially rose with temperature, ranging from 0.37 to 1.53 g m−2 d−1 (Q10 = 2.4). Correspondingly, warming led to shallower oxygen penetration into the sediment, ranging from 4.12 to 2.08 mm. Denitrification rates increased with warming (Q10 = 2.6), ranging from 8.4 to 86 μmol N m−2 h−1. The results of this short-term experiment confirm the potential increase of denitrification with rising temperature, promoted by lower oxygen availability in the top layer of the sediment, which supports the understanding of denitrification variability in freshwaters.

Sediment-associated organic matter sources and sediment oxygen demand in a Special Area of Conservation (SAC): A case study of the River Axe, UK.

Oxygen demand in river substrates providing important habitats for the early life stages of aquatic ecology, including lithophilous fish, can arise due to the oxidation of sediment‐associated organic matter. Oxygen depletion associated with this component of river biogeochemical cycling, will, in part, depend on the sources of such material. A reconnaissance survey was therefore undertaken to assess the relative contributions from bed sediment‐associated organic matter sources potentially impacting on the River Axe Special Area of Conservation (SAC), in SW England. Source fingerprinting, including Monte Carlo uncertainty analysis, suggested that the relative frequency‐weighted average median source contributions ranged between 19% (uncertainty range 0–82%) and 64% (uncertainty range 0–99%) for farmyard manures or slurries, 4% (uncertainty range 0–49%) and 35% (uncertainty range 0–100%) for damaged road verges, 2% (uncertainty range 0–100%) and 68% (uncertainty range 0–100%) for decaying instream vegetation, and 2% (full uncertainty range 0–15%) and 6% (uncertainty range 0–48%) for human septic waste. A reconnaissance survey of sediment oxygen demand (SOD) along the channel designated as a SAC yielded a mean SOD5 of 4 mg O2 g−1 dry sediment and a corresponding SOD20 of 7 mg O2 g−1 dry sediment, compared with respective ranges of 1–15 and 2–30 mg O2 g−1 dry sediment, measured by the authors for a range of river types across the UK. The findings of the reconnaissance survey were used in an agency (SW region) catchment appraisal exercise for informing targeted management to help protect the SAC.

A numerical analysis of biogeochemical controls with physical modulation on hypoxia during summer in the Pearl River estuary

Abstract. A three-dimensional (3-D) physical–biogeochemical coupled model was applied to explore the mechanisms controlling the dissolved oxygen (DO) dynamics and bottom hypoxia during summer in the Pearl River estuary (PRE). By using the numerical oxygen tracers, we proposed a new method (namely the physical modulation method) to quantify the contributions of boundary conditions and each source and sink process occurring in local and adjacent waters to the DO conditions. A mass balance analysis of DO based on the physical modulation method indicated that the DO conditions at the bottom layer were mainly controlled by the source and sink processes, among which the sediment oxygen demand (SOD) at the water–sediment interface and the re-aeration at the air–sea interface were the two primary processes determining the spatial extent and duration of bottom hypoxia in the PRE. The SOD could cause a significant decrease in the bottom DO concentrations (averaged over July–August 2006) by over 4 mg L−1 on the shelf off the Modaomen sub-estuary, leading to the formation of a high-frequency zone of hypoxia (HFZ). However, the hypoxia that occurred in the HFZ was intermittent and distributed in a small area due to the combined effects of re-aeration and photosynthesis, which behaved as sources for DO and offset a portion of the DO consumed by SOD. The bottom DO concentrations to the west of the lower Lingdingyang Bay (i.e. the western shoal near Qi'ao Island) were also largely affected by high SOD, but there was no hypoxia occurring there because of the influence of re-aeration. Specifically, re-aeration could lead to an increase in the bottom DO concentrations by ∼ 4.8 mg L−1 to the west of the lower Lingdingyang Bay. The re-aeration led to a strong vertical DO gradient between the surface and the lower layers. As a result, the majority (∼ 89 %) of DO supplemented by re-aeration was transported to the lower layers through vertical diffusion and ∼ 28 % reached the bottom eventually. Additional numerical experiments showed that turning off re-aeration could lead to an expansion of the hypoxic area from 237 to 2203 km2 and result in persistent hypoxia (hypoxic frequency > 80 %) to the west of the lower Lingdingyang Bay. Compared to re-aeration and SOD, photosynthesis and water column respiration had relatively small impacts on the DO conditions; turning off these two processes increased the hypoxic area to 591 km2. In summary, our study explicitly elucidated the interactive impacts of physical and biogeochemical processes on the DO dynamics in the PRE, which is critical to understanding hypoxia in this shallow and river-dominated estuarine system.

The Chaoborus pump: Migrating phantom midge larvae sustain hypolimnetic oxygen deficiency and nutrient internal loading in lakes

Hypolimnetic oxygen demand in lakes is often assumed to be driven mainly by sediment microbial processes, while the role of Chaoborus larvae, which are prevalent in eutrophic lakes with hypoxic to anoxic bottoms, has been overlooked. We experimentally measured the respiration rates of C. flavicans at different temperatures yielding a Q10 of 1.44–1.71 and a respiratory quotient of 0.84–0.98. Applying the experimental data in a system analytical approach, we showed that migrating Chaoborus larvae can significantly add to the water column and sediment oxygen demand, and contribute to the observed linear relationship between water column respiration and depth. The estimated phosphorus excretion by Chaoborus in sediment is comparable in magnitude to the required phosphorus loading for eutrophication. Migrating Chaoborus larvae thereby essentially trap nutrients between the water column and the sediment, and this continuous internal loading of nutrients would delay lake remediation even when external inputs are stopped.

Extremely high sulfate reduction, sediment oxygen demand and benthic nutrient flux associated with a large-scale artificial dyke and its implication to benthic-pelagic coupling in the Yeongsan River estuary, Yellow Sea

We investigated environmental impact of large-scale dyke on the sediment geochemistry, sulfate reduction rates (SRRs), sediment oxygen demand (SOD) and potential contribution of benthic nutrient flux (BNF) to primary production in the Yeongsan River estuary, Yellow Sea. The sediment near the dyke (YE1) with high organic carbon (Corg) content (>4%, dry wt.) was characterized by extremely high SOD (327mmolm−2d−1) and SRRs (91–140mmolm−2d−1). The sulfate reduction accounted for 73% of Corg oxidation, and was responsible for strikingly high concentrations of NH4+ (7.7mM), PO43− (67μM) and HS− (487μM) in pore water. The BNF at YE1 accounted for approximately 200% of N and P required for primary production in the water column. The results present one of the most extreme cases that the construction of an artificial dyke may have profound impacts on the biogeochemical and ecological processes in coastal ecosystems.

Contribution of sediment oxygen demand to hypoxia development off the Changjiang Estuary

This study evaluates the contribution of sediment oxygen demand (SOD) to hypoxia development off the Changjiang Estuary based on SOD measurements from onboard chamber incubations and numerical experiments. Onboard core incubations were conducted for samples collected from four stations in the Yellow Sea (YS) and the East China Sea (ECS) during cruises in June, August and October 2006. The measured SOD ranges widely from 9.1 to 62.5 mmol O2 m−2 d−1 with a mean rate of 22.6 ± 16.4 mmol O2 m−2 d−1, and the maximum occurring in August. The rates in regions experiencing hypoxia vary from 13.5 to 24.0 mmol O2 m−2 d−1 with a mean of 18.9 ± 4.6 mmol O2 m−2 d−1. Additionally, the vertical oxygen flux was calculated from profile measurements at a hypoxic mooring station adjacent to the Changjiang Estuary on September 3rd and 4th, 2006. The oxygen flux across the pycnocline was about 3.1 mmol O2 m−2 d−1, much lower than the SOD, implying that the low oxygen supply associated with stratification promotes the formation and maintenance of hypoxia in bottom waters. The one-dimensional numerical experiments configured for stratified and well-mixed water columns further confirm that stratification is necessary for the development and persistence of hypoxia, while SOD is a major oxygen sink below the pycnocline. Integrated over June to August, the amount of oxygen loss beneath the pycnocline due to SOD is equal to 116%–148%, 80%–142% and 82%–179% of the total net oxygen loss in the southern hypoxic region, northern hypoxic region and the middle shelf, respectively. During June to August when hypoxia develops, SOD in the northern and southern regions has similar magnitude. The Changjiang Diluted Water (CDW) promotes hypoxia formation in both regions, while the oxygen advection caused by the Taiwan Warm Current (TWC) would alleviate hypoxia formation especially for the southern hypoxic region.

The impact of suspended oyster farming on nitrogen cycling and nitrous oxide production in a sub-tropical Australian estuary

In this study we quantified nitrate (NO3−) reduction (denitrification, anammox and DNRA) and N2O production in sediments and epibiont communities associated with Sydney Rock Oyster (Saccostrea glomerata) farming. In sediments beneath an active suspended oyster farm, DNRA accounted for 98% of NO3− reduction with rates of up to 169 ± 45 μmol N m−2 h−1. Much of this DNRA was fuelled by NO3− derived from nitrification. Reference sediments had significantly lower DNRA rates of 83.8 ± 28.2 μmol N m−2 h−1, however this constituted 96% of the sites total NO3− reduction. Fatty acid analysis showed that sediment organic matter was more labile in the oyster impacted sediments, facilitating subtle shifts in sediment oxygen demand which increased the Fe2+ availability with respect to the reference sediments. The difference in DNRA rate between the sites was attributed to autotrophic oxidation of soluble Fe2+ in sediments underlying the oyster cultures. DNRA was absent in the oyster shell epibiont communities and rates of anammox and denitrification were lower than in the sediments. Production of NH4+ from the oysters and their associated epibionts was larger than DNRA and reached a rate of 206.2 μmol N m−2 h−1. Nitrous oxide production rates were generally low compared to other aquaculture systems and the net flux of N2O for the combined oyster cultivation system (i.e. sediments plus epibionts) was negative, i.e. there was N2O consumption in the sediments beneath the oysters. Overall, subtropical suspended oyster farming systems favour inorganic N retention over N loss.

Variable reactivity of particulate organic matter in a global ocean biogeochemical model

Abstract. The marine biological carbon pump is dominated by the vertical transfer of particulate organic carbon (POC) from the surface ocean to its interior. The efficiency of this transfer plays an important role in controlling the amount of atmospheric carbon that is sequestered in the ocean. Furthermore, the abundance and composition of POC is critical for the removal of numerous trace elements by scavenging, a number of which, such as iron, are essential for the growth of marine organisms, including phytoplankton. Observations and laboratory experiments have shown that POC is composed of numerous organic compounds that can have very different reactivities. However, this variable reactivity of POC has never been extensively considered, especially in modelling studies. Here, we introduced in the global ocean biogeochemical model NEMO-PISCES a description of the variable composition of POC based on the theoretical reactivity continuum model proposed by Boudreau and Ruddick (1991). Our model experiments show that accounting for a variable lability of POC increases POC concentrations in the ocean's interior by 1 to 2 orders of magnitude. This increase is mainly the consequence of a better preservation of small particles that sink slowly from the surface. Comparison with observations is significantly improved both in abundance and in size distribution. Furthermore, the amount of carbon that reaches the sediments is increased by more than a factor of 2, which is in better agreement with global estimates of the sediment oxygen demand. The impact on the major macronutrients (nitrate and phosphate) remains modest. However, iron (Fe) distribution is strongly altered, especially in the upper mesopelagic zone as a result of more intense scavenging: vertical gradients in Fe are milder in the upper ocean, which appears to be closer to observations. Thus, our study shows that the variable lability of POC can play a critical role in the marine biogeochemical cycles which advocates for more dedicated in situ and laboratory experiments.

A decline in benthic algal production may explain recent hypoxic events in Lake Erie's central basin

Abstract Since the late 1990s, the central basin of Lake Erie has reputedly experienced an increase in the frequency and severity of hypoxic events. However, total phosphorus (TP) loading, in-lake TP concentrations, chlorophyll a (Chl a ), and sediment oxygen demand (SOD) have all declined in the central basin since the 1970s. Water clarity in this basin has declined from the 1970s to 2000s despite the invasion of dreissenid mussels around 1990. In shallow lakes, declines in benthic primary production (PP) can generate positive feedback loops between the internal loading of nutrients/dissolved organic carbon and hypoxic/anoxic conditions in the water column. Such a hypoxia-inducing mechanism driven by declines in benthic PP has not been explored in Lake Erie. To test if a decline in benthic PP might explain hypoxic events in the central basin of Lake Erie, we calculated the inter-decadal changes in benthic and planktonic algal production in this basin from the 1970s to the 2000s. Primary production models using water column Chl a concentrations and light attenuation indicated that benthic PP represents roughly 10% of the basin's total areal PP. However, our calculations show that benthic PP declined from approximately 540 to 200 g C/m 2 y since the 1970s. We propose that a decline in benthic PP may have played a key mechanistic role in the transition from externally-induced hypoxia (i.e. watershed nutrient loading fueling phytoplankton production) in the 1970s and 80s to internally-induced hypoxia (sediment resuspension and internal loading) since the late 1990s.

Seasonal Variation in Sediment Oxygen Demand in a Northern Chained River-Lake System

Sediment oxygen demand (SOD) contributes immensely to hypolimnetic oxygen depletion. SOD rates thus play a key role in aquatic ecosystems’ health predictions. These rates, however, can be very expensive to sample. Moreover, determination of SOD rates by sediment diagenesis modeling may require very large datasets, or may not be easily adapted to complex aquatic systems. Water quality modeling for northern aquatic systems is emerging and little is known about the seasonal trends of SOD rates for complex aquatic systems. In this study, the seasonal trend of SOD rates for a northern chained river-lake system has been assessed through the calibration of a water quality model. Model calibration and validation showed good agreement with field measurements. Results of the study show that, in the riverine section, SOD20 rates decreased from 1.9 to 0.79 g/m2/day as urban effluent traveled along the river while a SOD20 rate of 2.2 g/m2/day was observed in the lakes. Seasonally, the SOD20 rates in summer were three times higher than those in winter for both river and lakes. The results of the study provide insights to the seasonal trend of SOD rates especially for northern rivers and lakes and can, thus, be useful for more complex water quality modeling studies in the region.

Sediment oxygen demand and bottom sediment environment in the northern part of the North Basin of Lake Biwa, Japan

Sediment oxygen demand and bottom sediment environment in the northern part of the North Basin of Lake Biwa, Japan

Modelling Dissolved Oxygen/Sediment Oxygen Demand under Ice in a Shallow Eutrophic Prairie Reservoir

Dissolved oxygen is an influential factor of aquatic ecosystem health. Future predictions of oxygen deficits are paramount for maintaining water quality. Oxygen demands depend greatly on a waterbody’s attributes. A large sediment–water interface relative to volume means sediment oxygen demand has greater influence in shallow systems. In shallow, ice-covered waterbodies the potential for winter anoxia is high. Water quality models offer two options for modelling sediment oxygen demand: a zero-order constant rate, or a sediment diagenesis model. The constant rate is unrepresentative of a real system, yet a diagenesis model is difficult to parameterise and calibrate without data. We use the water quality model CE-QUAL-W2 to increase the complexity of a zero-order sediment compartment with limited data. We model summer and winter conditions individually to capture decay rates under-ice. Using a semi-automated calibration method, we find an annual pattern in sediment oxygen demand that follows the trend of chlorophyll-a concentrations in a shallow, eutrophic Prairie reservoir. We use chlorophyll-a as a proxy for estimation of summer oxygen demand and winter decay. We show that winter sediment oxygen demand is dependent on the previous summer’s maximum chlorophyll-a concentrations.

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 < 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.

Baseline biogeochemical data from Australia's continental margin links seabed sediments to water column characteristics

Surficial marine sediments are an important source of nutrients for productivity and biodiversity, yet the biogeochemistry of these sediments is poorly known in Australia. Seabed samples were collected at >350 locations in Australia’s western, northern and eastern continental margins during Federal Government surveys (2007–14). Parameters analysed included measures of organic matter (OM) source (δ13C, δ15N and C:N ratios), concentration (percentage total organic carbon,%TOC, and surface area-normalised TOC, OC:SA) and bioavailability (chlorin indices, total reactive chlorins, total oxygen uptake, total sediment metabolism (TSM), sediment oxygen demand (SOD) and SOD and TSM normalised against TOC). The aim of the present study was to summarise these biogeochemical ‘baseline’ data and make contextualised inferences about processes that govern the observed concentrations. The OM was primarily from marine sources and the OC:SA broadly reflected water column productivity (based on Moderate Resolution Imaging Spectroradiometer, MODIS). Approximately 40% of sediments were organic poor by global standards, reflecting seawater oligotrophy; ~12% were organic rich due to benthic production, high water column productivity and pockmark formation. OM freshness varied due to pigment degradation in water columns and dilution with refractory OM in reworked sediments. δ15N values confirmed the importance of N2 fixation to Timor Sea productivity, and point to recycling of fixed nitrogen within food chains in Western Australia.

Evaluation of Eutrophication Control Through Hypolimnetic Oxygenation

The accumulation of nutrients in water bodies occur due to excessive phosphorus and nitrogen loads from the catchments and other external sources, causing buildup of nutrients in sediments. Often, water bodies that present thermal stratification, experience depletion of dissolved oxygen (DO) in the hypolimnion, thereby causing anoxic conditions, favoring the release of nutrients and leading to eutrophic conditions. The use of hypolimnetic oxygenation systems (HOS), which can supply over 50mg/L of DO in the hypolimnion of deeper water bodies, has demonstrated to reverse these conditions in lakes and reservoirs in North America, Europe, and Australia. The objective of this study was to develop a model for forecasting the remediation progress of a eutrophied reservoir using HOS. For this purpose, a mass-balance model was developed that calculates the oxygen accumulation in water bodies, using experimentally obtained oxygen demand (OD) of water and sediment from the reservoir, the extracted OD, the external load of OD, DO provided by natural sources such as photosynthesis and interaction with the atmosphere, and DO supplied by the HOS. The model was applied to forecast DO concentrations in the hypolimnion of a Mexican reservoir under different scenarios of external load of OD and hypolimnetic oxygenation.

湖沼における底泥酸素消費量測定法の開発と湖沼環境評価への応用

本研究では, 湖沼における新環境基準項目となる底層溶存酸素 (DO) の変動と密接に関係する底泥の酸素消費量 (SOD) の新規測定手法を開発した。本手法は, 表層構造を保った底泥のSOD測定が可能, 既存手法に比べ測定が短時間, 現地測定が可能という利点を有する。本手法を用いて, 霞ヶ浦, 琵琶湖北湖と南湖において, 各湖のSODの差や季節変動を明らかにした。琵琶湖南湖の水生植物繁茂水域では, SOD測定開始から急激なDO消費が観測され, 嫌気的環境下で底泥溶出する還元型の鉄やマンガンによるDO消費が推察された。しかし, 各湖の底泥中の鉄, マンガン含量とSODに有意な相関は見られなかった。一方, SOD測定後の直上水の分析から, 底泥溶出する鉄・リン量とSODの有意な相関が明らかとなった。本手法はSOD測定の改善に加え, 還元型金属イオンのSODへの影響評価も見込めるため, 湖沼環境研究の進展に貢献することが期待される。