Sediment Nutrient Dynamics Research Articles

The determining factors of sediment nutrient content and stoichiometry along profile depth in seasonal water

In the recent decades, the area of seasonal water (SEW) has substantially increased at the global scale. To evaluate nutrient dynamics in aquatic ecosystems, previous studies have analyzed the determining factors of sediment nutrient content and stoichiometry on whole sediment profiles without depth separation on SEW sites. Such a methodology assumes that SEW sediment is a uniform unit and its nutrient dynamics are regulated by the same mechanism at various depths (uniformity assumption). We tested this assumption using sediment samples from six depth increments of 154 sediment profiles (1 m depth) on SEW sites at Shengjin Lake in subtropical China. We measured sediment total nitrogen (STN), total phosphorus (STP), nutrient fractions, and the molar ratio of STN to STP (RSNP), and investigated their determining factors at various depths. STN, STP, and RSNP were averaged at 1.34 g/kg, 0.55 g/kg, and 5.43, respectively, and all gradually decreased with depth. STN was positively affected by moisture and flooding duration in all depth increments. Instead, the major determining factors of STP changed from particle size at 0–20 cm of depth to pH and electrical conductivity at 30–100 cm of depth. These vertical patterns have close connections with sediment nutrient fractions since sediment N fractions did not shift along profile depths (i.e., over 99 % of STN was organic N) but sediment P fractions did (the percentage of Fe-P and Al-P decreased by 6.25 % but those of Ca-P increased by 4.31 % along the sediment depth gradient). The major determining factors of RSNP showed no obvious vertical patterns because they frequently varied along depth gradients. The results demonstrate that SEW sediment is not a uniform unit and the determining factors of nutrient dynamics change with depth. Our study highlights the importance of improved methodological reflection in studies addressing sediment nutrient dynamics on SEW sites.

Riparian Forest Cover Modulates Phosphorus Storage and Nitrogen Cycling in Agricultural Stream Sediments.

Watershed land cover affects in-stream water quality and sediment nutrient dynamics. The presence of natural land cover in the riparian zone can reduce the negative effects of agricultural land use on water quality; however, literature evaluating the effects of natural riparian land cover on stream sediment nutrient dynamics is scarce. The objective of this study was to assess if stream sediment phosphorus retention and nitrogen removal varies with riparian forest cover in agricultural watersheds. Stream sediment nutrient dynamics from 28 sites with mixed land cover were sampled three times during the growing season. Phosphorus dynamics and nitrification rates did not change considerably throughout the study period. Sediment total phosphorus concentrations and nitrification rates decreased as riparian forest cover increased likely due to a decline in fine, organic material. Denitrification rates were strongly correlated to surface water nitrate concentrations. Denitrification rate and denitrification enzyme activity decreased with an increase in forest cover during the first sampling period only. The first sampling period coincided with the greatest connectivity between the watershed and in-stream processing, indicating that riparian forest cover indirectly decreased denitrification rates by reducing the concentrations of dissolved nutrients entering the stream. This reduction in load may allow the sediment to maintain greater nitrogen removal efficiency, because bacteria are not saturated with nitrogen. Riparian forest cover also appeared to lessen the effect of agriculture in the watershed by decreasing the amount of fine material in the stream, resulting in reduced phosphorus storage in the stream sediment.

Bacterial Communities and Enzymatic Activities in Sediments of Long-Term Fish and Crab Aquaculture Ponds.

Aquaculture is among the most important and fastest growing agriculture sectors worldwide; however, it generates environmental impacts by introducing nutrient accumulations in ponds, which are possibly different and further result in complex biological processes in the sediments based on diverse farming practices. In this study, we investigated the effects of long-term farming practices of representative aquatic animals dominated by grass carp (GC, Ctenopharyngodon idella) or Chinese mitten crab (CMC, Eriocheir sinensis) on the bacterial community and enzyme activity of sediments from more than 15 years of aquaculture ponds, and the differences associated with sediment properties were explored in the two farming practices. Compared to CMC ponds, GC ponds had lower contents of TC, TN, and TP in sediments, and similar trends for sediment pH and moisture content. Sediment bacterial communities were significantly different between GC and CMC ponds, with higher bacterial richness and diversity in GC ponds. The bacterial communities among the pond sediments were closely associated with sediment pH, TC, and TN. Additionally, the results showed profoundly lower activities of β-1,4-glucosidase, leucine aminopeptidase, and phosphatase in the sediments of GC ponds than CMC ponds. Pearson’s correlation analysis further revealed strong positive correlations between the hydrolytic enzyme activities and nutrient concentrations among the aquaculture ponds, indicating microbial enzyme regulation response to sediment nutrient dynamics. Our study herein reveals that farming practices of fish and crab differently affect bacterial communities and enzymatic activities in pond sediments, suggesting nutrient-driven sediment biological processes in aquaculture ponds for different farming practices.

Impacts of bioturbation by Venus clam Cyclina sinensis (Gmelin, 1791) on benthic metabolism and sediment nutrient dynamics in a shrimp-clam polyculture pond

Dynamics of benthic inorganic nutrients are key biogeochemical components of sediment metabolism and ecosystems. This study investigated the roles of the bivalve Cyclina sinensis (Gmelin, 1791) and its influence on benthic metabolism, nutrient fluxes and sediment oxygen consumption (SOC) in a shrimp-clam polyculture system in comparison with shrimp culture ponds without incorporating clams, in Ningbo Zhejiang China. The benthic inorganic nutrients fluxes (ammonium-NH4+, nitrate plus nitrite-NO3-+NO2- and phosphate-PO43-) and SOC were measured across the sediment-water interface with dark incubation experiments. The results showed that there were significantly higher nutrient fluxes from the sediment into the overlying water (p<0.05) in the treatment ponds in the order of NH4+ > PO43- > NO3- + NO2-. The SOC varied significantly (p<0.05) and was three-times higher than that of the control ponds. Water quality (dissolved oxygen, pH, chlorophyll-a and salinity) recorded showed slight variations over time but were not significantly different (p>0.05) between the control and treatment ponds. Sediment organic matter and chlorophyll-a concentration measured in the shrimp-clam ponds varied significantly (p<.05) as compared to control ponds. The results of this study suggest that the bioturbation activities by C. sinensis promoted the SOC, sediment organic matter degradation and mineralisation process that increased the exchange of nutrients and oxygen uptake between the sediment and the overlying water.

Effects of invasive N2-fixing Acacia mearnsii on sediment nutrient concentrations in mountain streams: Implications of sediment geochemistry for ecosystem recovery

Widespread invasive nitrogen-fixing plant species pose major threats to water resources, biodiversity and nutrient dynamics of river catchments around the world. However, the impacts of invasive N2-fixing plants on in-stream sediment nutrient dynamics remain poorly understood. Here, we quantified the impacts of invasive N2-fixing Acacia mearnsii and A. mearnsii clearing on two mountain streams in South Africa’s Cape Floristic Region. Nutrients were measured in fine sediment that had infiltrated into the gravel bed and surface water in three reaches associated with natural fynbos shrubs, A. mearnsii invaded and cleared riparian ecotones. Results showed that the impacts of A. mearnsii invasions and Acacia clearing in riparian areas on in-stream sediment-associated nutrient concentrations are context-dependent. The difference in channel morphometry and sediment geochemical attributes at reach-scale contributed to the contrasting spatial patterns of sediment-adsorbed nutrients within these rivers. There was also an indication of a long-lasting effect of invasion on total phosphorus that could persist in river sediments ≥10 years after the removal of dense A. mearnsii stands in close proximity to streams. This could be a result of the complexation between phosphorus and immobile iron in sediment, resulting in the retention of ‘legacy phosphorus’. This underlines the importance of fine sediments in capturing nutrients and ultimately regulating nutrient concentrations in the water column.

Spatial distribution of sediment nitrogen and phosphorus in Lake Taihu from a hydrodynamics-induced transport perspective

Hydrodynamics play an important role in sediment nutrient dynamics in large shallow eutrophic lakes. In this study, the spatial patterns of sediment nitrogen and phosphorus in Lake Taihu were compared from a hydrodynamics-induced transport perspective based on high-resolution investigation of sediment, field observations, numerical simulations and long-term ecological data analysis. The results showed that sediments were primarily distributed in the west and southeast portions of the lake. Additionally, the total nitrogen (TN) and phosphorus (TP) stored in the active sediments was 166,329 t and 67,112.4 t, respectively. The sediment TN content was 319.4–3123.8 mg kg−1, with high content areas being primarily located in the Zhushan, Meiliang and East Taihu bays. The external nitrogen-containing nutrients in the overlying water, which is mostly dissolved nitrogen, can be horizontally transported by lake currents to the water areas with high biomass levels and weak vertical hydrodynamic disturbance where sediment nitrogen enrichment primarily occurs via bio-deposition. The sediment TP content ranged between 382.6 and 1314.1 mg kg−1, and the high content areas were primarily distributed near the inflowing river mouths. Sediment phosphorus enrichment primarily occurred via physical and chemical deposition. Surface waves caused vertical phosphorus transport from sediments to the overlying water but had a limited effect on its spatial distribution. Although the horizontal transport of phosphorus was found to be weaker than that of nitrogen, short-distance vertical transport of sediment phosphorus may relieve nutrient limitations, leading to maintenance of cyanobacterial blooms found in Lake Taihu.

Impact of water drawdown and rewetting on sediment nutrient-dynamics in a constructed delta-lake system (Oostvaardersplassen, The Netherlands): A mesocosm study

In densely populated delta regions, many freshwater shallow lakes constructed on top of marine deposits and their water tables are maintained at a fixed level. Reintroducing water table fluctuations in such lakes will stimulate emergent vegetation development, but potential alterations in nutrient fluxes are still largely unknown. In a mesocosm study, we investigated element fluxes between sediment and pore-water during water drawdown and over the sediment-water interface during subsequent rewetting using sediments from the Oostvaardersplassen (The Netherlands). Desiccation of lake sediment resulted in a decline in pore-water phosphate concentrations (up to 90%), while this was not observed for shore sediments with a desiccation history. Rewetting induced a strong flux of released sulphate and calcium over the sediment-water interface, while expected fluxes of phosphate and nitrogen to the surface water remained limited. In shore sediment, lower element fluxes were observed compared to lake sediments. While water drawdown in delta lakes on marine clay resulted in vegetation development, it can also induce in changes in buffering capacity of the sediment. This should be taken into account when applying water drawdown as a cyclic measure to regenerate emergent vegetation in constructed delta lakes.

Nutrient dynamics in core sediments of an artificial basal medium prepared with steelmaking slag and dredged materials

The availability of steelmaking slag, an industrial by-product, was examined as a component of a basal medium for the creation and regeneration of shallow habitats in coastal ecosystems. We investigated nutrient dynamics in sediments prepared with slag and dredged materials by conducting a core incubation experiment for 379 days. Silica sand was used as the reference material. Although slag caused alkalization of pore water, the pH in the surface layer recovered within a few days. The use of slag had limited influence on the dissolved inorganic nitrogen content, but pore water phosphate concentrations were considerably suppressed in slag-based media, especially when the pH was high. Nutrient diffusion fluxes from slag- and sand-based sediment cores were comparable to those in natural coastal environments. After 379 days, more than 90 % of the nutrients remained in the top 5 cm of the cores. Moreover, the sustained release of nutrients from basal media prepared with slag may play an important role in sustaining the productivity of macrophytobenthic ecosystems, including seagrass meadows. The mesocosm-scale experiment we proposed could evaluate long-term variations of nutrient dynamics in the artificial basal media. Because of wide variations in chemical properties among the different types of slag and dredged materials, approaches similar to this study may be essential before any large-scale application to marine environments.

Nutrient dynamics in 3 morphological different tropical seagrasses and their sediments

Seasonality of nutrient dynamics in three morphologically different seagrass species and their sediments was examined for 1 year between November 2006 and November 2007 at four sites in the Andaman Sea, Thailand. The smaller species, Cymodocea serrulata and Halophila ovalis, showed major seasonal variation in shoot density, above- and belowground biomass, much more than expected from seasonal changes in water temperature and light conditions. All parameters showed minimum values in the dry season due to desiccation during neap tides. In contrast Enhalus acoroides showed less seasonal variation. Only limited seasonality was found in tissue N content of all species, whereas tissue P content responded to the low P concentration in the water column during the wet season. There were no differences in sediment conditions among species, and nutrient pools were generally low. Furthermore there were no significant spatial differences in seagrass and sediment nutrient dynamics, despite varying anthropogenic activity at the study sites, reflecting the oligotrophic conditions in this region.

The effects of human activities and extreme meteorological events on sediment nitrogen dynamics in an urban estuary, Escambia Bay, Florida, USA

This study examined how sediment-sorbed PCBs and several large storms affected sediment nutrient dynamics based on potential nitrification rates and benthic flux measurements. PCBs were hypothesized to negatively affect potential nitrification rates due to the sensitivity of nitrifying bacteria. Sediment disturbance caused by the succession of storms, which can enhance nutrient inputs and phytoplankton production, was hypothesized to enhance both potential nitrification rates and benthic flux measurements as a result of higher nutrient and organic matter concentrations. Potential nitrification rates, benthic fluxes (NO3 − + NO2 −, NH4 +, and DIP), sediment PCB content, water content, organic content, salinity, bottom water dissolved oxygen, and sediment chlorophyll were measured at 13 different sites in Escambia Bay during the summer of 2005. Potential nitrification rates were highest at deep, organic-rich sites. Total PCB content did not have a direct effect on potential nitrification rates. An analysis of recent changes in benthic processes in relation to extreme meteorological events was performed by comparing the 2005 results with data from 2000, 2003, and 2004. Storm effects on sediment biogeochemistry were mixed with sediment nitrogen dynamics enhanced at some sites but not others. In addition, SOC and NH4 + fluxes increased in deeper channel sites after Hurricanes Ivan and Dennis, which could be attributed to the deposition of phytoplankton blooms. Sediment nutrient dynamics in Escambia Bay appear to be resilient to these extreme meteorological events since there were no significant effects on sediment processes in the Bay as a whole.

The Impact of Benthic Macrofauna for Nutrient Fluxes from Baltic Sea Sediments

This article focuses on the ecological role of benthic macrofauna on nutrient dynamics and benthic-pelagic coupling in the Baltic Sea with relation to eutrophication. Generally, benthic macrofaunal activities have large effects on sediment biogeochemistry and often with stimulatory effects on processes that counteract eutrophication, i.e., denitrification and increased phosphorus retention of the sediment. The degree of faunal impact on such processes varies depending on faunal density and functional group composition. The effect of macrofaunal activities on sediment nutrient dynamics can also result in a higher nitrogen: phosporus ratio of the sediments efflux compared with sediments without macrofauna. Increased internal nutrient loading during eutrophication-induced anoxia is suggested to be caused both by altered sediment biogeochemical processes and through reduced or lost bioturbating macrofauna and thereby a reduced stimulatory effect from their activities on natural purification processes of the Baltic Sea ecosystem.

RELATING EFFECT AND RESPONSE TRAITS IN SUBMERSED AQUATIC MACROPHYTES

Reliably predicting the consequences of short- or long-term changes in the environment is important as anthropogenic pressures are increasingly stressing the world's ecosystems. One approach is to examine the manner in which biota respond to changes in the environment ("response traits") and how biota, in turn, affect ecosystem processes ("effect traits"). I compared the response and effect traits of four submersed aquatic macrophytes to understand how water level management may affect wetland plant populations and ecosystem processes. I measured resource properties (nutrients in sediment and water), non-resource properties (pH, alkalinity, sediment temperature, oxygen production), and biotic properties (periphyton biomass) in replicated outdoor monocultures of Stuckenia pectinata, Potamogeton nodosus, P. crispus, and Zannichellia palustris. After seven weeks, three of eight replicates of each species treatment were subjected to a temporary water draw-down that desiccated aboveground plant parts. The four species differed in their effects on ecosystem properties associated with nutrient uptake and photosynthetic activity. Shoot growth rate was negatively correlated with light transmittance to the sediment surface whereas root growth rate and root:shoot ratio were correlated with a species' ability to deplete nutrients in sediment interstitial water. Occupation of space in the water column was correlated with water alkalinity and pH and with sediment temperature. Root growth rate was related simultaneously to species effects on sediment nutrient dynamics and recovery of ecosystem properties after water draw-down. This suggests that this morphological trait may be used to predict the effects of environmental change on ecosystem functioning within the context of water level management. Expanding these analyses to more species, different environmental stressors, and across aquatic and terrestrial ecosystems should enhance predictions of the complex effects of global environmental change on ecosystem functioning.

Coping with Uncertainty: A Case Study in Sediment Transport and Nutrient Load Analysis

We present a computational approach for identifying the significance of uncertainty in assessing the consequences of sediment and nutrient transport in a section of the Chattahoochee River south of Lake Lanier, as it passes through Atlanta, Georgia. Specifically, our analysis aims at identifying the key control and management actions, and the key scientific uncertainties about the fluvial system, that govern the attainment of a set of water quality objectives for the downstream boundary of the study area. To this end, we present a computational framework that integrates a recently developed sediment-nutrient dynamics model with a Monte Carlo-based methodology for model uncertainty evaluation. Our results suggest that, in general, reliable execution of controls and management actions is more crucial to meeting the target values for flow, sediment, and phosphorus concentration, than the scientific uncertainties associated with fluvial processes within the river channel. We also discuss the potential utility of our framework for accommodating the various science- and policy-derived uncertainties in the total maximum daily load process.

Effects of community structure on the seagrass Thalassia testudinum

The influence of community structure on the seagrass Thalassia testudinum was studied in 3 distinct communities low and high density monocultures, and patches intermixed with Halodule wrightii, in Cockroach Bay, Tampa, Florida. T. testudinum shoot-specific leaf mass and growth were significantly higher in low density monocultures, and both variables were negatively correlated with short-shoot density, Intraspecific, competition-density effects in high-density seagrass beds may be responsible for the relatively lower shoot-specific leaf mass and growth rates, possibly due to the reduction of available light from dense leaf canopies. These observations are supported by significantly higher T. testudinum leat C:N and δ 13 C in low density monocultures, which suggests that high rates of growth are coupled with high C and N demands and reduced discrimination of C. Lower T testudinum shoot-specific leaf mass and growth in mixed species patches may be partially explained by interspecific competition with H. wrightii, however, the exact mechanisms by which these species interact were not discovered. Differences among communities in sediment NH 4 + and PO 4 3- , and T. testudinum leaf C:N:P and δ 15 N suggest that community structure in seagrass meadows plays an important role in sediment nutrient dynamics and, potentially, nutrient availability. However, low leaf C:N and C:P ratios suggest that nutrients are not limiting in this system. This study shows that intraspecific competition, and to a lesser degree, interspecific interactions with H. wrightii, are important determinants of T testudinum productivity and potentially, seagrass community structure in Cockroach Bay.

Modelling the effects of macrophytes on algal blooming in eutrophic shallow lakes

A dynamic model for eutrophication incorporating phytoplankton and nutrients in the overlying water, submerged macrophytes Potamogeton pectinatus L., and nutrient dynamics in sediments was developed as a functional tool to understand the effects of macrophytes on algal blooming in shallow lakes. The submodule for the overlying water treats three types of phytoplankton (diatoms, green and blue green algae), the macro-nutrients, as well as dissolved oxygen in the water, while the macrophyte submodule consists of equations for the time-dependence of the macrophyte components: shoots, secondary shoots, roots, tubers, and new tubers. The sediment submodule describes the concentrations of detritus, nitrates, ammonium, dissolved oxygen, and phosphates. These modules are processed simultaneously. The model was applied to the Lake Veluwe (Netherlands) experiment, successfully reproducing the seasonal changes in the lake, such as the transition of the dominant species of phytoplankton from diatoms during spring, green algae in summer, to blue green algae in late autumn depending on the nutrient and light condition, nutrient concentration in the water, and the yearly life-cycle of macrophytes. The model also describes the long term transition in the lake: after artificial flushing with water rich in nitrates and calcium, the return flux from the sediment decreased, and together with the reduction in the external load, the phosphate concentration in the overlying water decreased. This lessened the phytoplankton biomass in the water, which resulted in the remarkable development of macrophytes under the improved light condition. Sensitivity analyses of important coefficients indicated that the maximum photosynthesis and respiration rate are the most sensitive parameters for macrophyte and algal development. The parameters have sufficient accuracy to be successfully applied to other experiments.

The effects of flushing with NO3 and Ca rich water on shallow eutrophic lakes

A long term computational results and sensitivity analysis of the eutrophication model, incorporating phytoplankton, submerged macrophytes and nutrient dynamics in sediments were performed for understanding the effects of macrophytes on algal blooming in shallow lakes. The model was successfully reproducing long term change experienced in Lake Veluwe (The Netherlands). The model also described the reduction of phosphate return flux from the sediment and phytoplankton biomass and the resulting development of macrophytes under improved light condition after restoration measurement of the lake by artificial flushing of nitrate rich water into the lake and reduction of external phosphorus loading. Numerical experiments reproduced the following phenomena successfully: the blooming after the initiation of macrophyte growth has a remarkable effect on the following macrophyte development, thus with higher nutrient load, the macrophytes are significantly depressed. Sensitivity analysis of important coefficients show that the maximum photosynthesis rate, the conversion rate from oxygen to ash free dry weight are most sensitive parameters for macrophyte and algal development.

Modeling of macrophytes and their effects on algal blooming in a shallow eutrophic lake

An eutrophication model, incorporating phytoplankton, submerged macrophytes and nutrient dynamics in sediments was developed to be a functional tool for understanding the effects of macrophytes on algal blooming in shallow lakes. The model was applied to the Lake Veluwe experiment, successfully reproducing seasonal change in the lake, such as the transition of the dominant species of phytoplankton from diatom during spring, green algae in summer, and to blue green in late autumn depending on the nutrient and light condition, nutrient concentration in the water, as well as the yearly life-cycle of macrophytes.

Effects of suspended mussel culture (Mytilus spp.) on sedimentation, benthic respiration and sediment nutrient dynamics in a coastal bay

Effects of suspended mussel culture (Mytilus spp.) on sedimentation, benthic respiration and sediment nutrient dynamics in a coastal bay

Nutrient Dynamics in Great Lakes Coastal Wetlands: Future Directions

The most comprehensive investigations of N and P dynamics in Great Lakes coastal wetlands have been done at Old Woman Creek National Estuarine Research Reserve (OWC); whether OWC is a good general model of coastal freshwater wetlands remains to be shown. This wetland is probably a nutrient sink, storing P in sediments (at least temporarily) and releasing N by dissimilatory denitrification. Also, its biotic community transforms dissolved inorganic N and P inputs into organic dissolved and particulate outputs, thereby altering nutrient availability to Lake Erie communities. Nutrient dynamics in coastal wetlands probably differs greatly from that of inland marshes (where slow decomposition rates permit peat to accumulate as a nutrient sink) and estuaries (where high salinity alters sediment nutrient dynamics). A conceptual model specific for coastal wetlands is presented that accounts for the wide range of redox potentials encountered over the short vertical span of the shallow OWC wetland ecosystem. Future studies need to be conducted within the context of testable hypotheses generated from this model. Future investigations should focus attention on annualized nutrient budgets, sediment-water nutrient exchanges and their dependence on organic matter generated within the ecosystem.