Tidal Freshwater Region Research Articles

Carbon storage and sediment trapping by Egeria densa Planch., a globally invasive, freshwater macrophyte

Invasive plants have long been recognized for altering ecosystem properties, but their long-term impacts on ecosystem processes remain largely unknown. In this study, we determined the impact of Egeria densa Planch, a globally invasive freshwater macrophyte, on sedimentation processes in a large tidal freshwater region. We measured carbon accumulation (CARs) and inorganic sedimentation rates in submerged aquatic vegetation SAV dominated by E. densa and compared these rates to those of adjacent tidal freshwater marshes. Study sites were chosen along a range of hydrodynamic conditions in the Sacramento-San Joaquin Delta of California, USA, where E. densa has been widespread since 1990. Cores were analyzed for bulk density, % inorganic matter, % organic carbon, 210Pb, and 137Cs. Our results show that E. densa patches constitute sinks for both “blue carbon” and inorganic sediment. Compared to marshes, E. densa patches have greater inorganic sedimentation rates (E. densa: 1103–5989 g m−2 yr−1, marsh: 393–1001 g m−2 yr−1, p < 0.01) and vertical accretion rates (E. densa: 0.4–1.3 cm yr−1, marsh: 0.3–0.5 cm yr−1, p < 0.05), but similar CARs (E. densa: 59–242 g C m−2 yr−1, marsh: 109–169 g C m−2 yr−1, p > 0.05). Sediment stored by E. densa likely reduces the resilience of adjacent marshes by depleting the sediment available for marsh-building. Because of its harmful traits, E. densa is not a suitable candidate for mitigating carbon pollution; however, currently invaded habitats may already contain a meaningful component of regional carbon budgets. Our results strongly suggest that E. densa patches are sinks for carbon and inorganic sediment throughout its global range, raising questions about how invasive SAV is altering biogeochemical cycling and sediment dynamics across freshwater ecosystems.

Trapping of Suspended Sediment by Submerged Aquatic Vegetation in a Tidal Freshwater Region: Field Observations and Long-Term Trends

Widespread invasion by non-native, submerged aquatic vegetation (SAV) may modify the sediment budget of an estuary, reducing the availability of inorganic sediment required by marshes to maintain their position in the tidal frame. The instantaneous trapping rate of suspended sediment in SAV patches in an estuary has not previously been quantified via field observations. In this study, flows of water and suspended sediment through patches of invasive SAV were measured at three tidally forced, freshwater sites, all located within the Sacramento-San Joaquin Delta in California. An acoustic Doppler current profiler deployed from a roving vessel provided velocity and backscatter data used to quantify fluxes of both water and suspended sediment. Sediment trapping efficiency, defined as instantaneous net trapped flux divided by incident flux, was positive in 24 of 29 cases, averaging + 5%. Coupled with 3 years of measured sediment flux data at one site, this suggests that trapping averages 3.7 kg m−2 year−1. This estimate compares favorably with the mean mass accumulation rate of 3.8 kg m−2 year−1 estimated from dated sediment cores collected at the study sites. Long-term measurements made upstream reveal a strong negative trend (− 1.8% year−1) in suspended sediment concentration, and intra-annual changes in both suspended sediment concentration and percent fines. The large footprint and high spatial density of invasive SAV coupled with declining sediment supply are diminishing downstream suspended sediment concentrations, potentially reducing the resiliency of marshes in the Delta and lower estuary to future sea-level rise.

An analytical phytoplankton model and its application in the tidal freshwater James River

This study constructs an analytical model to understand the phytoplankton dynamics in a one-dimensional system by integrating physical and biological processes. We present an analytical solution of phytoplankton distribution along the longitudinal direction of a tidal river. The solution has two components: water age and accumulative growth. The water age represents the overall effect of physical transport due to advection, while the accumulative growth represents the accumulation of phytoplankton biomass due to biological processes during the transport. In addition, an alternative solution with nonlinear reaction term is given to account for the feedback mechanism of nonlinear processes that affect phytoplankton growth rate. The nonlinear reaction term can be also used to approximate the effect of physical mixing on phytoplankton distribution. The analytical solutions can be further used to predict the temporal variation and spatial distribution of phytoplankton along the tidal river. They also serve as a mathematical tool to unite different field phytoplankton observations. We applied the model in the Tidal Freshwater Region (TFR) of James River under different dynamic conditions and the model results match well with the observations, which validates the theory on different time scales. Furthermore, an analysis is conducted for the Local Chlorophyll-a Maximum (LCM) in the TFR. It shows that the condition for LCM is biologically controlled, but its location is regulated by river flow and river geomorphology.

Physical and Biological Responses to Flow in a Tidal Freshwater Slough Complex

Author(s): Frantzich, Jared; Sommer, Ted; Schreier, Brian | Abstract: Although brackish marsh has been the subject of decades of research, tidal freshwater regions are still poorly understood. To provide insight into spatial and temporal dynamics of nutrients, physical conditions, and the plankton community in freshwater tidal habitat, we investigated from 2011 to 2014 a remnant freshwater tidal slough complex located in the Sacramento–San Joaquin Delta region of the San Francisco Estuary. Our results suggest that the tidal slough complex showed different seasonal nutrient, physical, and biological conditions when compared to a relatively homogenous adjacent large river channel, the Sacramento River. The tidal slough complex also showed substantial spatial variability in habitat conditions compared to nearby main river channels. Nutrient dynamics in the tidal slough complex appear to be driven by a complex suite of factors, including inflow from upstream tributaries and tidal flows from the downstream reach of the Sacramento River. Chlorophyll a in the tidal sloughs responded more strongly to upstream flow pulses than other environmental variables. The tidal slough complex generated significantly higher levels of chlorophyll a than other freshwater regions of the Delta. The 2011 and 2012 results were especially notable because unusually large flow pulses through the tidal slough complex appear to have contributed to rare phytoplankton blooms in downstream areas of the Delta during the fall months. Moreover, the 2012 flow pulse stimulated higher trophic levels, because significantly higher levels of zooplankton were in the tidal slough complex after the flow event. These results have important implications for our understanding of the functioning of freshwater tidal habitat, and for the design of potential restoration projects in these regions.

Development of the Hydrodynamic Model for Long-Term Simulation of Water Quality Processes of the Tidal James River, Virginia

Harmful algal blooms (HABs) have frequently occurred in the James River. The State has convened a Scientific Advisory Panel (SAP) to review the James River chlorophyll-a standards. The SAP will conduct a scientific study to review the basis for setting the chlorophyll-a standards. To support the SAP study of chlorophyll-a standards, the State of Virginia has decided to develop a numerical modeling system that is capable of simulating phytoplankton and HABs. The modeling system includes a watershed model, a three-dimensional hydrodynamic model and water quality models. The focus of this study will be on the development and verification of the hydrodynamic model. In order to simulate the complex geometry of the James River, a high-resolution model has been implemented. The model has been calibrated for a long-term period of 23 years. A series of model experiments was conducted to evaluate the impact of forcings on dynamic simulation and transport time. It was found that freshwater discharge is the most sensitive for an accurate simulation of salinity and transport time. The water age predicted by the model in the tidal freshwater region represents the fluctuation of transport processes, and it has a good correlation with the algal bloom, while at the downstream, the transport time simulation agrees with the delay of the HAB in the mesohaline of the James after the HAB occurred in the Elizabeth River due to the transport processes. The results indicate that the hydrodynamic model is capable of simulating the dynamic processes of the James and driving water quality models in the James River.

Increasing Severity of Phytoplankton Nutrient Limitation Following Reductions in Point Source Inputs to the Tidal Freshwater Segment of the James River Estuary

We conducted monthly bioassay experiments to characterize light and nutrient use efficiency of phytoplankton communities from the chlorophyll-a maximum located in the tidal freshwater region of the James River Estuary. Bioassay results were interpreted in the context of seasonal and inter-annual variation in nutrient delivery and biomass yield using recent and long-term data. Bioassay experiments suggest that nutrient limitation of phytoplankton production has increased over the past 20 years coinciding with reductions in point source inputs and estuarine dissolved nutrient concentrations. Despite increasing nutrient stress, chlorophyll concentrations have not declined due to more efficient nutrient usage. Greater CHLa yield (per unit of N and P) may be due to feedback mechanisms by which the presence of toxin-producing cyanobacteria inhibits grazing by benthic and pelagic filter-feeders. Seasonal patterns in nutrient limitation indicate that phytoplankton in the James respond to variations in inflow concentrations of dissolved nutrients. This association gives rise to an atypical pattern whereby the severity of nutrient limitation diminishes with low discharge in late summer due to minimal dilution of local point sources inputs by riverine discharge. We suggest that this may be a common feature of estuaries located in proximity to urbanized areas.

Air‐water CO2 fluxes in the microtidal Neuse River Estuary, North Carolina

From June 2009 to July 2010, we conducted 27 continuous‐flow surveys of surface water CO2 partial pressure (pCO2) along the longitudinal axis of the Neuse River Estuary (NRE), North Carolina ranging from the tidal freshwater region to the polyhaline border with the Pamlico Sound. Lateral transects were also conducted at the borders of each of three hydrologically distinct sections. The pCO2 displayed considerable spatial‐temporal variability. Likewise, net air‐water CO2 fluxes showed high spatial and temporal variability, with a maximum [release] of 271 mmol C m−2 d−1 during high river flow conditions in fall and minimum [uptake] of −38 mmol C m−2 d−1 during wind‐driven, high primary productivity conditions in late spring. During high‐flow conditions, pCO2 generally decreased from the river mouth to the Pamlico Sound, similar to patterns seen in well‐mixed systems. During warm, low‐flow conditions, surface water pCO2 distributions were spatially variable and dissimilar to those patterns seen in most macrotidal, well‐mixed estuaries. The annual air‐water CO2 efflux from the study area was 4.7 mol C m−2 yr−1, an order of magnitude less than previously estimated for temperate estuaries. The CO2 fluxes observed in the NRE highlight the contrasts between macrotidal and microtidal systems and suggest that global estuarine CO2 emissions are likely overestimated by the current classification approaches. Scaling this lower efflux by the relative surface area of macrotidal and microtidal systems would reduce the global estuarine flux by 42%.

Water Quality within the York River Estuary

Key water quality management issues and threats within the Chesapeake Bay and its tidal tributaries include excess loadings of sediment and nutrients, and the introduction of toxic chemicals and microbial agents. Poor water clarity, principally controlled by suspended sediments and phytoplankton, is a persistent and widespread problem in the York River estuary with the oligohaline and middle mesohaline regions failing to meet submerged aquatic vegetation (SAV) habitat requirements (SAV criteria: ~10 NTU and TSS < 15 mg L−1). Both the primary and more localized secondary estuarine turbidity maximum are associated with these regions where elevated surface (30–35 mg L−1) and bottom (80–105 mg L−1) water TSS levels are observed. While nonpoint agriculture sources dominate riverine sediment load inputs, tidal and nearshore erosion are a significant source of suspended sediment in the York River estuary. As with sediment, nonpoint agricultural sources dominate nutrient inputs and streamflow is a dominant controlling factor in explaining variability in annual loads. Within mainstem surface waters, TDN and TDP concentrations exhibit a decreasing trend with increasing salinity. TDN and TDP concentrations are on the order of 40–45 μmol L−1 and 1.2 μmol L−1, respectively, in the tidal freshwater reaches of the Pamunkey and Mattaponi Rivers and 22–24 μmol L−1 and 0.6 μmol L−1 in the polyhaline regions of the York River. Mean DON exhibits little variation between salinity regimes. Seasonal phytoplankton biomass and productivity vary between salinity regimes with mean monthly peak chlorophyll a concentrations on the order of 9–10 μg L−1 in the tidal freshwater reaches, 14–18 μg L−1 in the transition zone below the freshwater region, 25–28 μg L−1 in the upper and middle mesohaline reaches, and 15 μg L−1 in the lower mesopolyhaline region. Based on DIN:DIP molar ratios and limited nutrient enrichment studies, tidal freshwater regions experience year-round phosphorus limitation, shifting to seasonal nitrogen limitation in the lower oligo, meso and polyhaline regions of the York River. Harmful algal bloom (HAB) producing dinoflagelletes have resulted in “red tides” that generally occur annually (summer, early fall) in the lower York River. With respect to low dissolved oxygen levels, hypoxia derived from oxidation of organic matter and sediment oxygen demand has also been observed repeatedly in the bottom waters of the lower, high salinity reaches when water temperatures exceed 20 °C. While studies have indicated limited toxic chemical contamination, mercury and PCB fish consumption advisories and restrictions have been issued within the York River estuary. Mercury impacted regions of the Mattaponi and Pamunkey Rivers receive significant wetland drainage that can enhance the potential for bioaccumulation of mercury in fish. Sediments in the York River proper exhibit PCB levels ranging from 1–5 ppb with more elevated levels (25 ppb) being observed in some contributing tidal creeks. In contrast to mercury where atmospheric deposition is a primary pathway, PCBs are generally released into the environment from runoff processes occurring at hazardous waste sites. With varying sources of fecal pollution, 20 percent (31.1 km2) of the York River's assessed shellfish waters has been designated as impaired. Condemned waters are restricted to major industrial and defense facility sites, and contributing smaller tidal creek systems.

English

Movements of pelagic organisms in the tidal freshwater regions of estuaries are sensitive to the movements of water. In the Sacramento-San Joaquin Delta—the tidal freshwater reach of the San Francisco Estuary—such movements are key to losses of fish and other organisms to entrainment in large water-export facilities. We used the Delta Simulation Model-2 hydrodynamic model and its particle tracking model to examine the principal determinants of entrainment losses to the export facilities and how movement of fish through the Delta may be influenced by flow. We modeled 936 scenarios for 74 different conditions of flow, diversions, tides, and removable barriers to address seven questions regarding hydrodynamics and entrainment risk in the Delta. Tide had relatively small effects on fate and residence time of particles. Release location and hydrology interacted to control particle fate and residence time. The ratio of flow into the export facilities to freshwater flow into the Delta (export:inflow or EI ratio) was a useful predictor of entrainment probability if the model were allowed to run long enough to resolve particles’ ultimate fate. Agricultural diversions within the Delta increased total entrainment losses and altered local movement patterns. Removable barriers in channels of the southern Delta and gates in the Delta Cross Channel in the northern Delta had minor effects on particles released in the rivers above these channels. A simulation of losses of larval delta smelt showed substantial cumulative losses depending on both inflow and export flow. A simulation mimicking mark–recapture experiments on Chinook salmon smolts suggested that both inflow and export flow may be important factors determining survival of salmon in the upper estuary. To the extent that fish behave passively, this model is probably suitable for describing Delta-wide movement, but it is less suitable for smaller scales or alternative configurations of the Delta.

Effects of pre‐existing submersed vegetation and propagule pressure on the invasion success of Hydrilla verticillata

Summary With biological invasions causing widespread problems in ecosystems, methods to curb the colonization success of invasive species are needed. The effective management of invasive species will require an integrated approach that restores community structure and ecosystem processes while controlling propagule pressure of non‐native species. We tested the hypotheses that restoring native vegetation and minimizing propagule pressure of invasive species slows the establishment of an invader. In field and greenhouse experiments, we evaluated (i) the effects of a native submersed aquatic plant species, Vallisneria americana, on the colonization success of a non‐native species, Hydrilla verticillata; and (ii) the effects of H. verticillata propagule density on its colonization success. Results from the greenhouse experiment showed that V. americana decreased H. verticillata colonization through nutrient draw‐down in the water column of closed mesocosms, although data from the field experiment, located in a tidal freshwater region of Chesapeake Bay that is open to nutrient fluxes, suggested that V. americana did not negatively impact H. verticillata colonization. However, H. verticillata colonization was greater in a treatment of plastic V. americana look‐alikes, suggesting that the canopy of V. americana can physically capture H. verticillata fragments. Thus pre‐emption effects may be less clear in the field experiment because of complex interactions between competitive and facilitative effects in combination with continuous nutrient inputs from tides and rivers that do not allow nutrient draw‐down to levels experienced in the greenhouse. Greenhouse and field tests differed in the timing, duration and density of propagule inputs. However, irrespective of these differences, propagule pressure of the invader affected colonization success except in situations when the native species could draw‐down nutrients in closed greenhouse mesocosms. In that case, no propagules were able to colonize. Synthesis and applications. We have shown that reducing propagule pressure through targeted management should be considered to slow the spread of invasive species. This, in combination with restoration of native species, may be the best defence against non‐native species invasion. Thus a combined strategy of targeted control and promotion of native plant growth is likely to be the most sustainable and cost‐effective form of invasive species management.

Interannual variation in stable carbon and nitrogen isotope biogeochemistry of the Mattaponi River, Virginia

Seasonal and interannual variation of the stable carbon (C) and nitrogen (N) isotope composition of suspended particulate organic matter (POM) was measured in the brackish and tidal freshwater regions of the Mattaponi River, a tributary of the York River, Virginia, and a pristine end member on a continuum of anthropogenic modification within Chesapeake Bay. A principal components analysis indicated that seasonal variation was related to physical mixing and river discharge. Freshwater POM had high C : N (.12), depleted particulate organic carbon isotopic composition (d13CPOC, 226% to 230%), and depleted particulate nitrogen isotopic composition (d15NPN, 2–10%) compared to brackish water POM, which had lower C : N and enriched d13CPOC (224% to 227%) and d15NPN (7–15%). During high discharge events, the d13CPOC was enriched, the d15NPN depleted, and the C : N high relative to low discharge periods, indicating a large contribution from terrestrial-derived material. Within tidal freshwater, POM was comprised of humic-rich sediment, vascular plant matter, and phytoplankton produced in situ. Nonconservative mixing behavior was observed. Endogenously produced phytoplankton increased POC concentrations in tidal freshwater and oligohaline portions during base flows. Where estuarine and riverine POM mixed, the isotopic composition of the POM was homogenized, blurring source-specific characters observed upriver and thereby emphasizing the need to characterize the freshwater end member of estuaries carefully in order to identify POM sources. In estuaries, identifying the origin of particulate organic matter (POM) is difficult because POM is received from multiple sources, including riparian vegetation, adjacent marsh vegetation, submerged and emergent aquatic vegetation and associated epiphytes, and phytoplankton produced in situ. Early research using the stable isotope composition of estuarine POM to identify its dominant origins and fates led investigators to conclude that estuarine phytoplankton and terrestrial material were the major contributors to estuarine organic matter (OM; dissolved and particulate fractions) and that these sources

Temporal variability in sources of dissolved organic carbon in the lower Mississippi river

Here we report on the temporal changes in the composition of dissolved organic carbon (DOC) collected in the tidal freshwater region of the lower Mississippi River. Lignin-phenols, bulk stable carbon isotopes, compound-specific isotope analyses (CSIA) and 13C nuclear magnetic resonance (NMR) spectrometry were used to examine the composition of high molecular weight dissolved organic matter (HMW DOM) at one station in the lower river over 6 different flow regimes in 1998 and 1999. It was estimated that the annual input of DOC delivered to the Gulf of Mexico from the Mississippi River was of 3.1 × 10 −3 Pg, which represents 1.2% of the total global input of DOC from rivers to the ocean. Average DOC and HMW DOC were 489 ±163 and 115 ± 47 μM, respectively. 13C-NMR spectra revealed considerably more aliphatic structures than aromatic carbons in HMW DOC. Lignin phenols were significantly 13C-depleted with respect to bulk HMW DOM indicating that C 4 grass inputs to the HMW DOM were not significant. It is speculated that C 4 organic matter in the river is not being converted (via microbial decay) to HMW DOM as readily as C 3 organic matter is, because of the association of C 4 organic matter with finer sediments. The predominantly aliphatic 13C NMR signature of HMW DOM suggests that autochthonous production in the river may be more important as a source of DOC than previously thought. Increases in nutrient loading and decreases in the suspended load (because of dams) in the Mississippi River, as well as other large rivers around the world, has resulted in significant changes in the sources and overall cycling of riverine DOC.

Spatial and temporal variation of the nekton and hyperbenthos from a temperate European estuary with regulated freshwater inflow

The aquatic macrofauna of the Guadalquivir estuary were sampled (1 mm mesh persiana net) at 5 sampling sites located along the entire (except the tidal freshwater region) estuarine gradient of salinity (outer 50 km). A total of 134 fish and macroinvertebrate species was collected but only 62 were considered common or regularly present in the estuary. Univariate measures of the community structure showed statistically significant differences among sampling sites: species richness, abundance, and biomass decreased in the upstream direction, being positively correlated with the salinity. Temporal differences of these three variables were also statistically significant. While a clear seasonal pattern (minimum densities in winter and maximum in spring-summer) was observed for abundance and biomass, no such pattern existed for the number of species. Mysids was the most dominant group throughout the estuary (96% to 99% of abundance; 49% to 85% of biomass), although fish biomass was also important at the outer estuary (36% to 38%). Multivariate analyses indicated highly significant spatial variation in the macrofaunal communities observed along the salinity gradient. These analyses suggest that the underlying structure was a continuum with more or less overlapping distributions of the species dependent on their ability to tolerate different physicochemical conditions. There were also significant temporal (intermonthly + interannual) variation of the estuarine community; the relative multivariate dispersion indicated that monthly variation was more considerable (relative multivariate dispersion >1) at the outer part of the estuary during the wet year (last 20 km) and was higher in the inner stations during the dry year (32 to 50 km from the river mouth). Since a clear negative exponential relationship was observed between the freshwater input (from a dam located 110 km upstream) and water salinity at all sampling stations, it is concluded that the human freshwater management is probably affecting the studied estuarine communities. While the higher seasonal (long-term) stability of the salinity gradient, due to the human control of the freshwater input, may facilitate the recruitment of marine species juveniles during the meteorologically unstable early-spring, the additional (short-term) salinity fluctuations during the warm period may negatively affect species that complete their lifecycle within the estuary.

Spatial and Temporal Characteristics of Nutrient and Phytoplankton Dynamics in the York River Estuary, Virginia: Analyses of Long-Term Data

Ten years (1985–1994) of data were analyzed to investigate general patterns of phytoplankton and nutrient dynamics, and to identify major factors controlling those dynamics in the York River Estuary, Virginia. Algal blooms were observed during winter-spring followed by smaller summer blooms. Peak phytoplankton biomass during the winter-spring blooms occurred in the mid reach of the mesohaline zone whereas peak phytoplankton biomass during the summer bloom occurred in the tidal fresh-mesohaline transition zone. River discharge appears to be the major factor controlling the location and timing of the winter-spring blooms and the relative degree of potential N and P limitation. Phytoplankton biomass in tidal fresh water regions was limited by high flushing rates. Water residence time was less than cell doubling time during high flow seasons. Positive correlations between PAR at 1 m depth and chlorophylla suggested light limitation of phytoplankton in the tidal fresh-mesohaline transition zone. Relationships of salinity difference between surface and bottom water with chlorophylla distribution suggested the importance of tidal mixing for phytoplankton dynamics in the mesohaline zone. Accumulation of phytoplankton biomass in the mesohaline zone was generally controlled by N with the nutrient supply provided by benthic or bottom water remineralization.

Long-term trends in the macrobenthos and water quality of the lower Chesapeake Bay (1985–1991)

Long-term trends in macrobenthic communities of the lower Chesapeake Bay, USA, were examined using data collected quarterly (March, June, September and December) from 1985 to 1991 at 16 stations along a salinity gradient from tidal freshwater regions of the major tributaries (James, York and Rappahannock rivers) to the polyhaline region of the main-stem of Chesapeake Bay. A non-parametric trend analysis procedure was applied to five parameters characterizing macrobenthic community structure: community biomass, species richness, abundance of individuals, proportion of biomass composed of opportunistic species (opportunistic biomass composition) and proportion of biomass composed of equilibrium species (equilibrium biomass composition). For the parameters tested 36 trends were detected. For community biomass, five trends were significant; all had positive slopes and occurred in the James and York rivers. For species richness, six trends were significant; all had positive slopes with three trends in the James River, two trends in the York River and one trend in the main-stem of Chesapeake Bay. For abundance of individuals, 17 trends were detected; all abundance trends were seasonally dependent, had positive slopes and occurred at 12 of the 16 stations. For opportunistic biomass composition, four trends were significant; all had positive slopes with one trend in the lower Rappahannock River and three trends in the main-stem of Chesapeake Bay. For equilibrium biomass composition four trends were significant; two trends had positive slopes (one in the James River and one in the York River) and two trends had negative slopes (one in the Rappahannock River and one in the main-stem of Chesapeake Bay). Trends in the James and York rivers were considered to indicate improving conditions for the benthos, while trends in the lower Rappahannock River and the main-stem of the Chesapeake Bay were considered to indicate deteriorating conditions. Deteriorating conditions for the benthos were associated with regions exposed to summer, low dissolved oxygen events. The trends in the indicators of benthic biological community health were inferentially related to trends observed in water quality conditions in the tributaries and main-stem of Chesapeake Bay. All major water quality and biotic trends appeared to correspond in an ecologically meaningful manner.

Cesium isotope-activity in the Weser ecosystem three years after the disaster at Chernobyl

In 1989, three years after the disaster at Chernobyl, the Cesium (Cs-137 and Cs-134) activity of water, sediments, suspended solids, algae, and crustaceans were studied in five sections of the Weser estuary covering the nontidal and tidal freshwater region down to the brackish area. The total water activities in the freshwater regions are similar, but there are differences in the Cs distribution between the dissolved and the particulate phase depending on the concentration of suspended solids and abiotic water parameters. The Cs activity derived from Chernobyl is only detectable in sediments and suspended solids. Specific differences in Cs accumulation were found for crustaceans but not for algae.