Particulate Nutrients Research Articles

Spatial distribution and trophic ecology of dominant copepods associated with turbidity maximum along the salinity gradient in a highly embayed estuarine system in Ariake Sea, Japan

The present study aimed to investigate into the feeding ecology of the dominant copepods along a salinity gradient in Chikugo estuary. Copepod composition was studied from samples collected from stations positioned along the salinity gradient of the estuary. Copepod gut pigment concentrations were measured by fluorescence technique and hydrographical parameters such as temperature, salinity, transparency, suspended particulate matter (SPM); pigments such as chlorophyll- a (Chl- a), phaeopigment; and particulate nutrients such as particulate organic carbon (POC) and particulate organic nitrogen (PON) were measured. Two distinct zones in terms of nutrient and pigment concentrations as well as copepod distribution and feeding were identified along the estuary. We identified a zone of turbidity maximum (TM) in the low saline upper estuary which was characterized by having higher SPM, higher POC and PON but lower POC:PON ratios, higher pigment concentrations but lower Chl- a/SPM ratios and higher copepod dry biomass. Sinocalanus sinensis was the single dominant copepod in low saline upper estuary where significantly higher concentrations of nutrients and pigments were recorded and a multispecies copepod assemblage dominated by common coastal copepods such as Acartia omorii, Oithona davisae and Paracalanus parvus was observed in the lower estuary where nutrient and pigment concentrations were lower. Copepods in the estuary are predominantly herbivorous, feeding primarily on pigment bearing plants. However, completely contrasting trophic environments were found in the upper and the lower estuary. It was speculated from the Chl- a and phaeopigment values that copepods in the upper estuary receive energy from a detritus-based food web while in the lower estuary an algal-based food web supports copepod growth. Overall, the upper estuary was identified to provide a better trophic environment for copepod and is associated with higher SPM concentrations and elevated turbidity. The study demonstrates the role of estuarine turbidity maximum (ETM) in habitat trophic richness for copepod feeding. The study points out the role of detritus-based food web as energy source for the endemic copepod S. sinensis in the upper estuary, which supports as nursery for many fish species.

Regional scale nutrient modelling: exports to the Great Barrier Reef World Heritage Area

Clearing of native vegetation and replacement with cropping and grazing systems has increased nutrient exports to the Great Barrier Reef (GBR) to a level many times the natural rate. We present a technique for modelling nutrient transport, based on material budgets of river systems, and use it to identify the patterns and sources of nutrients exported. The outputs of the model can then be used to help prioritise catchment areas and land uses for management and assess various management options. Hillslope erosion is the largest source of particulate nutrients because of its dominance as a sediment source and the higher nutrient concentrations on surface soils. Dissolved nutrient fractions contribute 30% of total nitrogen and 15% of total phosphorus inputs. Spatial patterns show the elevated dissolved inorganic nitrogen export in the wetter catchments, and the dominance of particulate N and P from soil erosion in coastal areas. This study has identified catchments with high levels of contribution to exports and targeting these should be a priority.

The cycling and fate of terrestrially-derived sediments and nutrients in the coastal zone of the Great Barrier Reef shelf

The coastal zone of the Great Barrier Reef shelf, with an area of 30,000 km 2 and a water volume of 300 km 3, receives an average annual input of sediment on the order of 14–28 Mt y −1––an estimated two- to fourfold increase since European settlement. There is considerable concern about the impact and ultimate fate of terrestrially-derived nutrients entering the Great Barrier Reef World Heritage Area (GBRWHA). Analysis of current data suggests that microbial communities in coastal waters and in unconsolidated sediments metabolise nutrients equivalent to the entire dissolved and particulate nutrient load debouched from land. River-derived nutrients account for 40–80% of the carbon, 13–30% of the nitrogen, and 2–5% of the phosphorus necessary to support the observed rates of benthic and pelagic mineralisation in Princess Charlotte Bay in the far north, and in Rockingham Bay and Missionary Bay in the central section, of the GBRWHA. Nearly all nitrogen is ultimately returned to the atmosphere via denitrification. There is little net burial of nutrients in subtidal sediments. These budget estimates are based on a sparse data set, but it is clear that marine sources of nutrients (N-fixation by pelagic and benthic cyanobacteria) must be important, but the magnitude of these sources is poorly known and likely to be highly variable in space and time. Data from sediment trap deployments suggest that, despite significant re-suspension, sedimentation fluxes are sufficient to balance benthic mineralisation rates. Most organic material deposited to the benthos appears to be flocculent or colloidal aggregates, perhaps formed via microbial mediation and exudation of extra-cellular material. The geophysical dynamics of the coastal boundary layer plays an important role in concentrating biological and biogeochemical activity within a shallow, narrow coastal zone. Mangroves and tidal flats are small in area, but trap, transform, and store a disproportionate amount of sediment and organic matter within the GBRWHA. The highly efficient use of terrestrially-derived nutrients by benthic and pelagic microbes in the coastal zone helps to explain why coral reefs on the middle and outer shelf have remained relatively unscathed despite a significant increase in sediment delivery.

Vertical gradient of nutrients in two dimictic lakes ? influence of phototrophic sulfur bacteria on nutrient balance

Vertical profiles of soluble and particulate nutrients were analyzed at the end of summer stratification in two dimictic lakes located in northeast Germany. In addition, irradiance and plankton biomass were determined. The concentrations of particulate organic carbon and phytoplankton biomass in the epilimnion were higher in Lake Tiefer than in Lake Dudinghausen, even though the apparent trophic status of Lake Tiefer was higher than Lake Dudinghausen. In Lake Dudinghausen, phototrophic sulfur bacteria accumulated in the hypolimnion between 8 and 10 m, whereas in Lake Tiefer low light penetration prevented the development of phototrophic bacteria in those horizons in which sulfide might be present. Because both lakes have anoxic hypolimnia, we assumed that in both cases phosphorus was released from the sediment into the hypolimnion. In Lake Tiefer, redox conditions and the presence of nitrate and nitrite limited the water depth range in which P-release occurred. In Lake Dudinghausen, part of the released soluble reactive phosphorus was incorporated into the phototrophic sulfur bacteria biomass and thus transformed to particulate phosphorus. As much as 70% of the particulate phosphorus in the hypolimnion was found in the phototrophic sulfur bacterial layer, with 15–20% of this particulate phosphorus consisting of polyphosphate storage compounds. The low ratio of soluble reactive phosphorus to particulate phosphorus in the hypolimnion was, therefore, attributed to phototrophic sulfur bacteria. The phototrophic sulfur bacteria appear to act as an internal nutrient filter and convert soluble reactive phosphorus into particulate phosphorus.

Transparency tube provides reliable water-quality measurements

We examined the efficacy of using transparency-tube measurements to estimate turbidity, total suspended solids (TSS) and particulate nitrogen and phosphorus concentrations in several California waterways. Just as lowering a black-and-white disk (Secchi disk) into a lake provides a convenient way to measure its water clarity, a transparency tube offers a practical alternative for measuring water clarity and suspended solids concentrations in California streams and waterways. While transparency relationships with turbidity and TSS are strongest within a given sampling location, these relationships are relatively robust across a wide range of water bodies displaying contrasting conditions. However, transparency-tube measurements appear to have limited value in predicting particulate nutrient concentrations, even at a given sampling site. The low cost, ease of use and excellent repeatability of measurement make the transparency tube a potentially valuable tool for anyone interested in monitoring water quality, including farmers, ranchers, citizen volunteer groups, schools and local governments seeking to get involved in watershed monitoring programs.

The nearshore phosphorus shunt: a consequence of ecosystem engineering by dreissenids in the Laurentian Great Lakes

Dreissenid mussels have been exceptionally successful invaders in North American lakes and rivers, especially in the lower Laurentian Great Lakes. As benthic filter feeders capable of attaching to hard substrates, the magnitudes of their biomass and filtering activity in nearshore waters are without precedent. The dreissenid colonization has implications for the removal and fate of materials filtered from the water by the mussels and for the longer-term development of the nearshore benthic community and lake ecosystem. A conceptual model, the nearshore shunt, seeks to describe a fundamental redirection of nutrient and energy flow consequent to dreissenid establishment. The model explains some emergent problems in the Great Lakes, such as reemergence of Cladophora in some coastal zones while offshore P concentrations remain low, and highlights areas in need of more research. The source of particulate nutrient inputs to dreissenids and the fate of materials exported from the benthic community are critical to understanding the role of dreissenids in the lakes and assessing the applicability of current models for managing nutrients and fisheries. The nearshore shunt would require even more stringent P management for lakes strongly impacted by dreissenids to maintain nearshore water quality.

Effects of macrograzers and light on periphyton stoichiometry

Ecological stoichiometry describes the biochemical constraints of trophic interactions emerging from the different nutrient content and nutrient demand of producers and consumers, respectively. Most research on this topic originates from well‐mixed pelagic food webs, whereas the idea has received far less attention in spatially structured habitats. Here, we test how light as well as grazing and nutrient regeneration by consumers affects growth and biomass of benthic primary producers. In the first laboratory experiment, we manipulated grazer presence (two different snail species plus ungrazed control), in the second experiment we factorially combined manipulation of grazer presence and light intensity. We monitored snail and periphyton biomass as well as dissolved and particulate nutrients (nitrogen and phosphorus) over time. Grazers significantly reduced algal biomass in both experiments. Grazers affected periphyton nutrient content depending on the prevailing nutrient limitation and their own body stoichiometry. In the nitrogen (N‐) limited first experiment, grazers increased N both in the periphyton and in the water column. The effect was stronger for grazers with lower N‐content. In the phosphorus (P‐) limited second experiment, grazers increased the P‐content of the periphyton, but the grazer with lower N‐content had additionally positive effects on algal N. Light reduction did not affect periphyton biomass, but increased chlorophyll‐, N‐ and P‐content of the periphyton. These experiments revealed that the indirect effects of grazers on periphyton were bound by stoichiometric constraints of nutrient incorporation and excretion.

Effects of sheep grazing episodes on sediment and nutrient loss in overland flow

The effect of sheep grazing on the loss of sediment and nutrients in overland flow was investigated on a hill-country farm in the Waikato, New Zealand. The losses were measured in runoff produced artificially with small (0.5 m2) and large (1050 m2) rainfall simulators. Immediately after intensive winter grazing, rainfall applied at high intensity increased concentrations by a factor of 13–16 for sediment and particulate nutrients, 33–76 for dissolved reactive phosphorus and ammonium-nitrogen, and 5–7 for dissolved organic nitrogen and phosphorus. During summer, when there was less removal of vegetative cover, there was a smaller effect of grazing. The concentrations of sediment and particulate nutrients in overland flow were strongly correlated with the percentage of bare ground. The concentrations returned to background levels within 6 weeks after grazing, and the infiltration rate and ground cover also recovered from grazing in this time. The small rainfall simulator experiments showed that the infiltration rate decreases with grazing, which results in greater runoff after grazing. The greater runoff combines with the increased concentrations to give higher loads after grazing. In late winter, the infiltration rates were approximately half the summer values and the soil erodibility was approximately double, so the risk of high sediment and nutrient loads is greatest in winter, especially considering the higher rainfall and lower grass growth. The management implications are that exposure of bare ground associated with intensive grazing should be avoided, especially in winter.

Effect of a flood underflow on reservoir water quality: Data and three-dimensional modeling

*As in many of the world's reservoirs, floods provide most of the water to Lake Burragorang (Sydney, Australia). In this study a winter flood through this large (2km 3 ), long (ca. 50km) and narrow (ca. 0.5-2km) reservoir was monitored at multiple stations over several weeks. The nutrient-laden underflow took 7-8 days to travel from the river confluence to the dam and upwardly displaced the pre-flood anoxic hypolimnion. Particulate phosphorus and nitrogen, and turbidity settled at an exponential rate (0.34-0.42 d -1 ) in the head of the underflow. Application of a three-dimensional model (ELCOM) with large grid sizes (200×200×1m) for reasonable run times (ca. 1 day) did not resolve the underflow hydrodynamics in this large, narrow and complex geometry. A technique for 'straightening' morphologies that are narrow and curvy was applied to the Lake Burragorang bathymetry to allow large model grid sizes. Simulations with the 'straightened' bathymetry had low run times and compared well with field data. Then, an aquatic ecological model (CAEDYM) was coupled to ELCOM to simulate the biogeochemical fate of the floodwaters. Simulated spatial patterns of dissolved oxygen, and filterable and particulate nutrients compared well with field data. Further, the ELCOM-CAEDYM simulation demonstrated that the dynamic spatial variations in water quality from a Eularian perspective during such flood events are dominated by transport. Settling is the dominant process in the head of the underflow from a Lagrangian frame of reference. To simulate spatial variations during a flood it is adequate to couple an accurate hydrodynamic driver to a simply configured hiogeochemical model.

Spatial and temporal variability in phytoplankton iron limitation along the California coast and consequences for Si, N, and C biogeochemistry

Iron limitation was investigated along the Northern California coast in the summer of 1999. Small‐volume (1 l) shipboard iron addition bottle experiments were performed at 44 stations to gain the greatest possible temporal and spatial coverage of the area. Parameters measured in these 4‐day incubations included size‐fractionated chlorophyll a and particulate nutrients (C, N, and Si). Degrees of community iron limitation were quantified and compared using various iron limitation indexes, calculated as the ratio of chlorophyll a, particulate organic nitrogen, or particulate organic carbon produced in Fe‐amended bottles to the amounts produced in controls. Iron limitation occurred most frequently and was most severe on stations off the continental shelf, away from sedimentary sources of iron, as well as during relaxation events in aged upwelled water. Size‐fractionated chlorophyll a data did not suggest large Fe‐mediated changes in phytoplankton community composition. Fe limitation reduced phytoplankton production of particulate organic nitrogen and carbon, but had much less effect on biogenic silica production. The result is an increase in particulate Si:N and Si:C ratios of control samples, which were frequently double those of Fe‐amended samples. Particulate C:N ratios also decreased under Fe limitation, indicating that iron availability exerts a strong control on C, N, and Si elemental composition of phytoplankton, and thus on the biogeochemical cycling of these nutrients in the California upwelling region.

The influence of fish cage aquaculture on pelagic carbon flow and water chemistry in tidally dominated mangrove estuaries of peninsular Malaysia

The impact of floating net cages culturing the seabass, Lates calcarifer, on planktonic processes and water chemistry in two heavily used mangrove estuaries in Malaysia was examined. Concentrations of dissolved inorganic and particulate nutrients were usually greater in cage vs. adjacent (≈100 m) non-cage waters, although most variability in water-column chemistry related to water depth and tides. There were few consistent differences in plankton abundance, production or respiration between cage and non-cage sites. Rates of primary production were low compared with rates of pelagic mineralization reflecting high suspended loads coupled with large inputs of organic matter from mangrove forests, fishing villages, fish cages, pig farms and other industries within the catchment. Our preliminary sampling did not reveal any large-scale eutrophication due to the cages. A crude estimate of the contribution of fish cage inputs to the estuaries shows that fish cages contribute only ≈2% of C but greater percentages of N (32–36%) and P (83–99%) to these waters relative to phytoplankton and mangrove inputs. Isolating and detecting impacts of cage culture in such heavily used waterways—a situation typical of most mangrove estuaries in Southeast Asia—are constrained by a background of large, highly variable fluxes of organic material derived from extensive mangrove forests and other human activities.

MODELING THE HYDROCHEMISTRY OF THE CANNONSVILLE WATERSHED WITH GENERALIZED WATERSHED LOADING FUNCTIONS (GWLF)1

ABSTRACT: A previous modeling study used the Generalized Watershed Loading Functions (GWLF) model to simulate stream‐flow, and nutrient and sediment loads to Cannonsville Reservoir from the West Branch Delaware River (WBDR). We made several model revisions, calibrated key parameters, and tested the original GWLF model and a revised GWLF model using more recent data. Model revisions included: addition of unsaturated leakage between unsaturated and saturated subsurface reservoirs; revised timing of sediment export; inclusion of urban sediments and dissolved nutrients; tracking of particulate nutrients from point sources; and revised timing of septic system loads. The revision of sediment yield timing resulted in significant improvements in monthly sediment and particulate phosphorus predictions as compared to the original model. Addition of unsaturated leakage improved hydrologic predictions during low flow months. The other model changes improve realism without adding significant model complexity or data requirements. Goodness of fit of revised model predictions versus stream measurements, as measured by the Nash‐Sutcliff coefficient of model efficiency, exceeded 0.8 for streamflow‐0.7 for sediment yield and dissolved nitrogen (N) and 0.6 for particulate and dissolved phosphorus (P). The revised GWLF model, with limited calibration, provides reasonable estimates of monthly streamflow, and nutrient and sediment loads in the Cannonsville watershed.

Hydrodynamic control of nitrogen and phosphorus turnover in an eutrophicated estuary in the Baltic

The turnover of phosphorus and nitrogen have been studied in a low salinity estuary in the Bothnian Sea. The estuary, Gårdsfjärden, has a high loading of nutrients from a pulp and paper mill which supplies the estuary with three times the annual natural input of phosphorus and nitrogen, respectively. The turnover of nutrients was to a great extent determined by hydrodynamic variations. During periods of intense resuspension there was a net export of particulate bound nutrients from the estuary to the sea but since these periods were short there was an overall net retention of particulate nutrients. The estuary was a source for dissolved phosphorus to the sea. The major source of phosphorus export was release of dissolved P from anoxic sediments. Gårdsfjärden was a sink for dissolved nitrogen which most likely escaped the estuary by denitrification. Nitrate was supplied by degradation of particulate organic nitrogen but the main source was import from the sea.

Concentration and transport of particulate nutrients and metals in the Lower Paraná River during extreme flooding

Fil: Villar, C.A.. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - La Plata. Instituto de Limnologia ; Argentina

Water column production and nutrient characteristics in mangrove creeks receiving shrimp farm effluent

Water column processes in undisturbed mangrove creeks and in creeks receiving effluent from shrimp farms in North Queensland, Australia, were studied. Small scale discharges into tidal creeks did not elevate dissolved nutrient concentrations compared with non-impacted creeks, but did elevate concentrations of particulate nutrients, chlorophyll and suspended solids proximal to the site of the effluent discharge. Rates of primary and bacterial production downstream from the discharge exceeded rates in the shrimp ponds because of the synergistic effects of turbulent mixing and eutrophication. In the lower reaches of the mangrove creeks and immediately offshore, standing stocks of particulate material and rates of primary and bacterial production were within the range of values found in non-discharge areas. Our results suggest that water column production by phytoplankton and bacteria strips nutrients from shrimp farm effluent and repackages them in more bioavailable forms.

Performance of a recirculating wetland filter designed to remove particulate phosphorus for restoration of Lake Apopka (Florida, USA)

Operation of a 14-km2 wetland filter for removal of total phosphorus (TP) from lake water is part of the restoration program for hypereutrophic Lake Apopka, Florida. This system differs from most treatment wetlands because 1) water is recirculated back to the lake, and 2) the goal is removal of particulate phosphorus (P), the dominant form of P in Lake Apopka. The operational plan for the wetland is maximization of the rate rather than the efficiency of P removal. The St. Johns River Water Management District operated a 2-km2 pilot-scale wetland to examine the capacity of a wetland system to remove suspended solids and particulate nutrients from Lake Apopka. TP in the inflow from Lake Apopka ranged from about 0.12 to 0.23 mg l(-1), and hydraulic loading rate (HLR) varied from 6.5 to 42 m yr(-1). The performance of the pilot-scale wetland supported earlier predictions. Mass removal efficiencies for TP varied between about 30% and 67%. A first-order, area-based model indicated a rate constant for TP removal of 55 m yr(-1). We compared actual removal of P with model predictions and used modeled performance to examine optimal operational conditions. Correspondence between observed and modeled outflow TP was not good with constant variable values. Monte Carlo techniques used to introduce realistic stochastic variability improved the fit. The model was used to project a maximal rate of P removal of about 4 g P m(-2) yr(-1) at P loading 10-15 g P m(-2) yr(-1) (HLR 60-90 m yr(-1)). Data from the pilot wetland indicated that actual rates of P removal may prove to be higher. Further operation of the wetland at high hydraulic and P loading rates is necessary to verify or modify the application of the model.

Community and connectivity: summary of a community based monitoring program set up to assess the movement of nutrients and sediments into the Great Barrier Reef during high flow events

The Great Barrier Reef (GBR) system encompasses the largest system of corals and related life forms anywhere in the world. The health of this extensive system, particularly the inshore area, is dependent on the relationship between the GBR and adjacent coastal catchments. The major impact of agricultural practices on the GBR is the degradation of water quality in receiving (rivers) waters, caused by increased inputs of nutrients, suspended sediments and other pollutants. For the past three years, the Great Barrier Reef Marine Park Authority (GBRMPA) has been involved with the co-ordination of a river-monitoring program, specifically targeting the sampling of rivers during flood events. Representative sites were set up along two North Queensland rivers, the Russell-Mulgrave and Barron Rivers. This monitoring program is run in conjunction with the Queensland Department of Natural Resources' Waterwatch program. The program involves intensive sampling of first flush, extreme flow and post flood conditions over the two rivers. Extreme flow conditions are sampled over a limited time span (48 hours) with trained volunteers at 4-hour intervals. Concentrations measured in the flood events are dependent on land use characteristic, and extent of flow. Concentrations of dissolved and particulate nutrients are higher if the extreme flow event is part of the first flush cycle. Concentrations of DIN and DIP measured before, during and after a major flood event suggest that there is a large storage of inorganic material within the Barron and Russell-Mulgrave agricultural subcatchments that move over a period of days, and perhaps weeks. This program created a forum in which GBRMPA liased with the Barron and Russell-Mulgrave community about the connectivity existing between the river and the Great Barrier Reef lagoon.

Dissolved and particulate nutrient flux from three adjacent agricultural watersheds: A five-year study

Fluxes of dissolved and particulate nitrogen (N) and phosphorus (P) from three adjacent watersheds were quantified with a high-resolution sampling program over a five-year period. The watersheds vary by an order of magnitude in area (12,875, 7968 and 1206 ha), and in all three watersheds intensive agriculture comprises > 90% of land. Annual fluxes of dissolved N and P per unit watershed area (export coefficients) varied ∼2X among watersheds, and patterns were not directly related to watershed size. Over the five-year period, mean annual flux of soluble reactive P (SRP) was 0.583 kg P · ha −1 · yr −1 from the smallest watershed and 0.295 kg P · ha −1 · yr −1 from the intermediate-sized watershed, which had the lowest SRP flux. Mean annual flux of nitrate was 20.53 kg N · ha −1 · yr −1 in the smallest watershed and 44.77 kg N · ha −1 · yr −1 in the intermediate-sized watershed, which had the highest nitrate flux. As a consequence, the export ratio of dissolved inorganic N to SRP varied from 80 (molar) in the smallest watershed to 335 in the intermediate-sized watershed. Because most N was exported as nitrate, differences among watersheds in total N flux were similar to those for nitrate. Hence, the total N:P export ratio was 42 (molar) for the smallest watershed and 109 for the intermediate-sized watershed. In contrast, there were no clear differences among watersheds in the export coefficients of particulate N, P, or carbon, even though > 50% of total P was exported as particulate P in all watersheds. All nutrient fractions were exported at higher rates in wet years than in dry years, but precipitation-driven variability in export coefficients was greater for particulate fractions than for dissolved fractions. Examination of hydrological regimes showed that, for all nutrient fractions, most export occurred during stormflow. However, the proportion of nitrate flux exported as baseflow was much greater than the proportion of SRP flux exported as baseflow, for all three watersheds (25-37% of nitrate exported as baseflow vs. 3-13% of SRP exported as baseflow). In addition, baseflow comprised a greater proportion of total discharge in the intermediate-sized watershed (43.7% of total discharge) than the other two watersheds (29.3 and 30.1%). Thus, higher nitrate export coefficients in the intermediate-sized watershed may have resulted from the greater contribution of baseflow in this watershed. Other factors potentially contributing to higher

A conceptual model of nutrient mobilisation and transport applicable at large catchment scales

A conceptual model of nutrient mobilisation and transport is presented and coupled to a hydrological model, LASCAM. The model predicts catchment export of diffuse-source soluble and particulate phosphorus, particulate nitrogen, nitrate-nitrogen and ammonium-nitrogen. It explicitly includes the nutrient cycling processes of sorption, mineralisation, leaching, fixation, volatilisation, nitrification, denitrification, plant uptake and harvest losses. Soluble nutrients are assumed to be mobilised by surface runoff and by baseflow discharge, while particulate nutrients are associated with surface erosion and the stream sediment transport processes of deposition, re-entrainment, bed degradation and settling. The nutrient model includes 29 optimisable parameters, 11 for phosphorus and 18 for nitrogen, although several of these can be prescribed from measurements or from the literature. The model is applied to two large subcatchments of the 120,000 km 2 Avon River basin in Western Australia and shown to provide good predictions of daily nutrient export in a long-term simulation.

Mathematical analysis on coexistence conditions of phytoplankton and bacteria systems with nutrient recycling

We analyzed a condition of dynamical coexistence of phytoplankton and bacteria in the model systems with nutrient recycling from the viewpoint of permanence. In this model, nutrients were classified into dissolved and particulate matter, and bacteria use not only particulate nutrient but also dissolved nutrient. We led the sufficient conditions of permanence in the model system. On the basis of these conditions, we studied how they can achieve the coexistence estimating indirect effects between phytoplankton and bacteria through nutrients, and argued the effects of nutrient recycling through bacterial decomposition on the coexistence. From these analysis, we obtained that coexistence conditions can be explained by invasion conditions, and coexistence can be achieved even if bacteria cannot always invade the steady state consisting of only two types of nutrient. The estimation of indirect effects indicated the mutualistic interactions between phytoplankton and bacteria under the conditions of permanence. This suggests that mutualistic situation will be occurred by nutrient recycling after sufficiently long time, even if phytoplankton and bacteria compete with each other through common resource initially.