Net Phytoplankton Growth Research Articles

Photo- and heterotrophic pico- and nanoplankton in the Mississippi River plume: distribution and grazing activity

The abundance of pico- and nanophytoplankton, bacteria and heterotrophic nanoflagellates, and grazing rates on phototrophic pico- and nanoplankton and bacterioplankton were assessed along a salinity gradient (0.2–34.4) in the Mississippi River plume in May 2000. Grazing rates were established by serial dilution experiments, and analysis by flow cytometry allowed differentiation of grazing rates for different phytoplankton subpopulations (eukaryotes, Synechococcus spp., Prochlorococcus spp.). Grazing rates on phytoplankton tended to increase along the salinity gradient and often approached or exceeded 1 day−1. Phytoplankton net growth rates (growth – grazing) were mostly negative, except for positive values for eukaryotic nanoplankton in the low-salinity, high-chlorophyll region. Grazing pressure on bacteria was moderate (∼0.5 day−1) and bacteria gained positive net growth rates of ∼0.3 day−1. Eukaryotic nanophytoplankton were the major phototrophic biomass and protozoan food source, contributing 30–80% of the total consumed carbon. Bacteria were the second most important food source at 9–48% of the total consumed carbon. Synechococcus spp. and Prochlorococcus spp. remained an insignificant portion of protozoan carbon consumption, probably due to their low contribution to the total pico- and nanoplankton biomass. Group-specific grazing losses relative to standing stocks suggest protozoan prey preference for eukaryotes over bacteria. Protozoan grazers exerted a major grazing pressure on pico- and nanophytoplankton, but less so on bacteria.

Dissolved inorganic phosphorus, dissolved iron, and Trichodesmium in the oligotrophic South China Sea

Dissolved inorganic phosphorus (DIP) concentrations in the oligotrophic surface waters of the South China Sea decrease from ∼20 nM in March 2000 to ∼5 nM in July 2000, in response to seasonal water column stratification. These minimum DIP concentrations are one order of magnitude higher than those in the P‐limited, iron‐replete stratified surface waters of the western North Atlantic, suggesting that the ecosystem in the South China Sea may be limited by bioavailable nitrogen or some trace nutrient rather than DIP. Nutrient enrichment experiments using either nitrate, phosphate or both indicate that nitrogen limits the net growth of phytoplankton in the South China Sea, at least during March and July 2000. The fixed nitrogen limitation may result from the excess phosphate (N:P<16) transported into the South China Sea from the North Pacific relative to microbial population needs, or from iron control of nitrogen fixation. The iron‐limited nitrogen fixation hypothesis is supported by the observation of low population densities of Trichodesmium spp. (<48 × 103 trichomes/m3), the putative N2 fixing cyanobacterium, and with low concentrations of dissolved iron (∼0.2–0.3 nM) in the South China Sea surface water. Our results suggest that nitrogen fixation can be limited by available iron even in regions with a high rate of atmospheric dust deposition such as in the South China Sea.

Dynamic global patterns of nitrate, phosphate, silicate, and iron availability and phytoplankton community composition from remote sensing data

Satellites routinely provide frequent, large‐scale, near‐surface views of many oceanographic variables pertinent to plankton ecology, but nutrient fertility remains problematic. A recently derived set of nitrate (N), phosphate (P), and silicate (S) nutrient depletion temperatures (NDT) were subtracted from AVHRR‐derived sea surface temperatures for March 1999 through June 2000 to determine eight categories of temporally varying N, P, and S presence/absence in the world ocean. Complementary midmonth, aerosol optical thickness (70°N to 70°S) and precipitation (40°N to 40°S), obtained from the AVHRR Pathfinder effort and the TRMM microwave imager, respectively, represented iron (F) presence (>10%)/absence (<10%) in the world ocean as dry and wet (40°N to 40°S) or just dry (40°N–70°N and 40°S–70°S) deposition of atmospheric dust. The resulting 16 N, P, S, and F presence/absence categories provided a dynamic view of seasonal and interannual nutrient variability in the world ocean. SeaWiFS chlorophyll a maps for April, July, and October 1999 and January 2000 were compared to the N, P, S, and F categories from these months. Phytoplankton cell size and taxonomic composition categories linked to each of the 16 nutrient availability categories translated the nutrient associations with chlorophyll a into an inferred phytoplankton community structure. Consideration of additional bottom‐up (like solar irradiance exposure) and top‐down (like grazing by zooplankton) influences on size and species/class specific net phytoplankton growth can improve the assignment of inferred phytoplankton community structure. The proposed dynamic approach toward monitoring nutrient availability can contribute to refined estimates of biogeochemical fluxes in the world ocean.

Effects of tidal shallowing and deepening on phytoplankton production dynamics: A modeling study

Processes influencing estuarine phytoplankton growth occur over a range of time scales, but many conceptual and numerical models of estuarine phytoplankton production dynamics neglect mechanisms occurring on the shorter (e.g., intratidal) time scales. We used a numerical model to explore the influence of short time-scale variability in phytoplankton sources and sinks on long-term growth in an idealized water column that shallows and deepens with the semidiurnal tide. Model results show that tidal fluctuations in water surface elevation can determine whether long-term phytoplankton growth is positive or negative. Hourly-scale interactions influencing weekly-scale to monthly-scale phytoplankton dynamics include intensification of the depth-averaged benthic grazing effect by water column shallowing and enhancement of water column photosynthesis when solar noon coincides with low tide. Photosynthesis and benthic consumption may modulate over biweekly time scales due to spring-neap fluctuations in tidal range and the 15-d cycle of solar noon-low tide phasing. If tidal range is a large fraction of mean water depth, then tidal shallowing and deepening may significantly influence net phytoplankton growth. In such a case, models or estimates of long-term phytoplankton production dynamics that neglect water surface fluctuations may overestimate or underestimate net growth and could even predict the wrong sign associated with net growth rate.

Dynamics of particulate dimethylsulphoniopropionate during a Lagrangian experiment in the northern North Sea

Abstract One of the key steps towards predicting dimethyl sulphide (DMS) emissions to the atmosphere is to understand the production and fate of its precursor, dimethylsulphoniopropionate (DMSP). This study used the framework of a SF 6 -Lagrangian experiment lasting 6 days, to examine the production and turnover of particulate DMSP (DMSPp) within a developing phytoplankton bloom characterised by abundant Emiliania huxleyi . Detailed information on the composition of the phytoplankton community and literature-derived estimates of cell DMSP content were used to partition DMSPp between 6 taxonomic groups. E. huxleyi was estimated to contribute an average of only 16% and 9% of the DMSPp standing stocks in surface and subsurface layers of the water column, respectively. Other phototrophs, including non-lithed nanoflagellates and dinoflagellates, in particular Prorocentrum minimum, made up a substantial proportion of the DMSPp, especially in the subsurface layer. The Lagrangian approach allowed a direct estimate of the net production of DMSPp, chlorophyll a and the 6 phytoplankton taxonomic groups in the surface layer. The net specific accumulation rate of DMSPp was 0.129 day −1 , equivalent to a net production of DMSPp over the 6 days of 37.3 nM averaged through the surface-layer depth. The net phytoplankton growth rate in terms of chlorophyll a was similar, at 0.108 day −1 . However, not all the phytoplankton showed a net growth during the 6 days, indicating that only certain taxa were responsible for the increases in DMSP and chlorophyll a . A significant relationship between 14 C primary production measurements and the potential production of DMSPp derived from dilution experiments was used to estimate an integrated ‘gross’ production and loss rate of DMSPp for the surface mixed layer. High DMSPp production rates were closely matched by high DMSPp loss rates. Ingestion by microzooplankton appeared to be the major cause of DMSPp loss, accounting for an average of 91% of the DMSPp disappearance. A large proportion of the ingested DMSPp was thought to be released as dissolved DMSP rather than DMS. An estimate of the total DMS flux to the atmosphere was equivalent to only 1.3% of the ‘gross’ DMSPp production in the surface layer during the developing phase of the phytoplankton bloom covered by this experiment. Other processes known to cause DMSP release from phytoplankton, such as viral lysis and senescence, may have become more important if the phytoplankton community had reached higher concentrations and/or encountered more growth-limiting conditions. However, in the present experiment horizontal and vertical mixing appeared to play a major role in determining the fate of the SF 6 -labelled water, and hence the progression of the phytoplankton community.

Inverse modeling of carbon and nitrogen flows in the pelagic food web of the northeast subarctic Pacific

We use inverse analysis to model carbon and nitrogen flows in the upper ocean food web at Ocean Station Papa (OSP; 50°N, 145°W) for winter, spring, and late summer. The seasonal variability in basic physical, chemical, and biological characteristics is low, and the particulate carbon and nitrogen flux at 200 m is remarkably constant. Despite this apparent uniformity, the food web structure undergoes significant seasonal changes. The diversity of trophic pathways is higher during late summer than during the other two periods. The spring ecosystem is not in steady state and undergoes net phytoplankton growth and macronutrient consumption. The microbial loop is well developed only during late summer. Nevertheless, ammonium regeneration by the food web seems insufficient to meet demand by the primary producers. The difference may be due to recycling of dissolved organic nitrogen (urea+free amino acids), a process not represented in the model. The winter food web is the closest to steady state, with nitrate utilisation approximately in balance with export of particulate nitrogen. The inverse analysis suggests two main seasonally invariant features of the NE Pacific ecosystem. First, the major trophic pathway is always from picophytoplankton (0.2–5 μm) to microzooplankton (heterotrophic dinoflagellates and ciliates) to mesozooplankton. This supports the idea of a strong coupling between the microbial and metazoan food webs. Second, much of the primary production (and bacterial production in late summer) is not grazed and is recycled through the detrital pool. Both these features seem to arise from the requirement to conserve nitrogen as well as carbon in the food web. More complete measurements on the microzooplankton 20–200 μm in size, including the small metazoans like nauplii larvae, are required to improve the models presented here.

Phytoplankton growth and mortality during the 1995 Northeast Monsoon and Spring Intermonsoon in the Arabian Sea

Phytoplankton growth rates and mortality rates were experimentally examined at eight stations in the Arabian Sea along the U.S. JGOFS cruise track during the 1995 Northeast Monsoon (January) and Spring Intermonsoon (March–April). Instantaneous growth rates averaged over an entire cruise were approximately twice as high during the NE Monsoon than during the Spring Intermonsoon period (overall averages of 0.84±0.29 (s.d.) versus 0.44±0.19 d −1). Average herbivore grazing (mortality) rates, however, were quite similar for the two seasons (overall averages of 0.35±0.18 and 0.30±0.17 d −1 for the NE Monsoon and Spring Intermonsoon, respectively). The absolute amounts of phytoplankton biomass consumed during each season also were similar (29 and 25% of standing stock consumed d −1 for the January and March–April cruises, respectively), as were the geographical trends of this removal. These seasonal trends in growth and removal rates resulted in net phytoplankton growth rates that were considerably higher during the January cruise (0.48 d −1) than during the March–April cruise (0.14 d −1). That is, phytoplankton production was more closely balanced during the Spring Intermonsoon season (87% of daily primary production consumed) relative to the NE Monsoon season (49% of daily primary production consumed). Station-to-station variability was high for rate measurements during either cruise. Nevertheless, there was a clear onshore–offshore trend in the absolute rate of removal of phytoplankton biomass (μg chlorophyll consumed l −1 d −1) during both cruises. Coastal stations had removal rates that were typically 2–4 times higher than removal rates at oceanic stations.

Temporal and vertical dynamics of phytoplankton net growth in Castle Lake, California

The impact of nutrient additions, zooplankton grazing and light intensity on phytoplankton net growth with depth and season was studied with five microcosm experiments in meso-oligotrophic, subalpine Castle Lake, California, during the period of summer stratification in June-September 1994. The incubations (4 day) were performed at 5 m intervals from the surface to the bottom using natural phytoplankton and zooplankton assemblages, with enrichments of phosphorus and nitrogen. The phytoplankton community was only limited by nutrients in the upper 5 m (epilimnion), as indicated by change in chlorophyll concentration. Nutrient enrichments had the greatest effect on the phytoplankton net growth in June and July. High light inhibited the phytoplankton net growth at the surface. Low light intensities limited phytoplankton at 20 m and below, and at the end of the growing season already around 10-15 m. A deep chlorophyll maximum in the hypolimnion in June-August was not limited by either light or nutrients. The results showed variation in grazers' impact on phytoplankton. These results suggest the importance of nutrient limitation only in the epilimnion with light inhibition at the surface, light limitation in the hypolimnion, and varying impact of zooplankton grazing in influencing the development of the phytoplankton in Castle Lake.

An iron‐based ecosystem model of the central equatorial Pacific

The central and eastern equatorial Pacific region is characterized by lower than expected phytoplankton biomass and primary production given the relatively high ambient nitrate concentrations. These unusual conditions have spawned several field programs and laboratory experiments to determine why this high nitrate‐low chlorophyll pattern persists in this region. To synthesize the results from these field programs, as well as providing additional evidence in support of the iron hypothesis, we developed a one‐dimensional, nine‐component ecosystem model of 0°N 140°W. The model components include two phytoplankton size fractions, two zooplankton size fractions, two detrital size fractions, dissolved iron, nitrate, and ammonium. The model was run for 5 years (1990–1994) and was forced using an atmospheric radiative transfer model, an ocean general circulation model (GCM), and in situ data. To our knowledge, this is the first ecosystem model at 0°N 140°W to synthesize the Joint Global Ocean Flux Study Equatorial Pacific Process Study (JGOFS EqPac) data set, as well as to use both in situ and modeled physical data to drive the model. Modeled phytoplankton, zooplankton, and iron all varied on interannual timescales due to El Niño events. Total phytoplankton biomass increased by as much as 40% from early 1992 (El Niño warm) to 1993 (normal). The results also indicate that the biomass increase during a cool period is not constant for each phytoplankton component, but instead the increase is most evident in the netphytoplankton (>10 μm). Netphytoplankton increase from a low of 0.1% of the total chlorophyll in 1992 to a high of 30% of the total in 1993. Microzooplankton grazing rates fluctuated in response to changes in nanophytoplankton growth rates, whereas mesozooplankton grazing was unrelated to netphytoplankton growth rates. The magnitude and temporal variability of phytoplankton chlorophyll agreed well with in situ data collected during 1992. Modeled primary production was lower than measured during El Niño but agreed with observations during normal conditions. The low primary productivity was probably a result of downwelling produced by the physical model. New production was calculated from total and recycled iron rather than nitrate‐based production and was more variable in general and almost 3 times the nitrate‐based new production during non‐El Niño conditions.

Processes governing phytoplankton blooms in estuaries. II:The role of horizontal transport

The development and distribution of phytoplankton blooms in estuaries are functions of both local conditions (i.e. the production-loss balance for a water column at a particular spatial location) and large-scale horizontal transport. In this study, the second of a 2-paper series, we use a depth-averaged hydrodynamic-biological model to identify transport-related mechanisms impacting phytoplankton biomass accumulation and distribution on a system level. We chose South San Francisco Bay as a model domain, since its combination of a deep channel surrounded by broad shoals is typical of drowned-river estuaries. Five general mechanisms involving interaction of horizontal transport with variability in local conditions are discussed. Residual (on the order of days to weeks) transport mechanisms affecting bloom development and location include residence time/export, import, and the role of deep channel regions as conduits for mass transport. Interactions occurring on tidal time scales, i.e. on the order of hours) include the phasing of lateral oscillatory tidal flow relative to temporal changes in local net phytoplankton growth rates, as well as lateral sloshing of shoal-derived biomass into deep channel regions during ebb and back into shallow regions during flood tide. Based on these results, we conclude that: (1) while local conditions control whether a bloom is possible, the combination of transport and spatial-temporal variability in local conditions determines if and where a bloom will actually occur; (2) tidal-time-scale physical-biological interactions provide important mechanisms for bloom development and evolution. As a result of both subtidal and tidal-time-scale transport processes, peak biomass may not be observed where local conditions are most favorable to phytoplankton production, and inherently unproductive areas may be regions of high biomass accumulation.

Does the Sverdrup critical depth model explain bloom dynamics in estuaries?

In this paper we use numerical models of coupled biological-hydrodynamic processes to search for general principles of bloom regulation in estuarine waters. We address three questions: What are the dynamics of stratie cation in coastal systems as ine uenced by variable freshwater input and tidal stirring? How does phytoplankton growth respond to these dynamics? Can the classical Sverdrup Critical Depth Model (SCDM) be used to predict the timing of bloom events in shallow coastal domains such as estuaries? We present results of simulation experiments which assume that vertical transport and net phytoplankton growth rates are horizontally homogeneous. In the present approach the temporally and spatially varying turbulent diffusivities for various stratie cation scenarios are calculated using a hydrodynamic code that includes the Mellor-Yamada 2.5 turbulence closure model. These diffusivities are then used in a time- and depth-dependent advection-diffusion equation, incorporating sources and sinks, for the phytoplankton biomass. Our modeling results show that, whereas persistent stratie cation greatly increases the probability of a bloom, semidiurnal periodic stratie cation does not increase the likelihood of a phytoplankton bloom over that of a constantly unstratie ed water column. Thus, for phytoplankton blooms, the physical regime of periodic stratie cation is closer to complete mixing than to persistent stratie cation. Furthermore, the details of persistent stratie cation are important: surface layer depth, thickness of the pycnocline, vertical density difference, and tidal current speed all weigh heavily in producing conditions which promote the onset of phytoplankton blooms. Our model results for shallow tidal systems do not conform to the classical concepts of stratie cation and blooms in deep pelagic systems. First, earlier studies (Riley, 1942, for example) suggest a monotonic increase in surface layer production as the surface layer shallows. Our model results suggest, however, a nonmonotonic relationship between phytoplankton population growth and surface layer depth, which results from a balance between several ‘ ‘ competing’ ’ processes, including the interaction of sinking with turbulent mixing and average net growth occurring within the surface layer. Second, we show that the traditional SCDM must be ree ned for application to energetic shallow systems or for systems in which surface layer mixing is not strong enough to counteract the sinking loss of phytoplankton. This need for ree nement arises because of the leakage of phytoplankton from the surface layer by turbulent diffusion and sinking, processes not considered in the classical SCDM. Our model shows that, even for low sinking rates and small turbulent

Interannual variability in spring bloom timing and magnitude in the Rhode River, Maryland, USA:observations and modeling

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 154:27-40 (1997) - doi:10.3354/meps154027 Interannual variability in spring bloom timing and magnitude in the Rhode River, Maryland, USA: observations and modeling Gallegos CL, Jordan TE, Correll DL The long-term average seasonal distribution of chlorophyll concentration in a central reach of the Rhode River estuary (Maryland, USA) has a peak in the spring of about 90 mg m-3. Here we examine interannual variability in chlorophyll and nutrient concentrations in recent years. Years are classified as having an average bloom, extraordinary bloom, or no bloom, and patterns of nutrient concentration are described for each category. To determine processes associated with the different categories of behavior, we performed a generalized sensitivity analysis of a model of nutrient-limited phytoplankton net growth which was previously shown to simulate the chlorophyll concentration and the observed pattern of shift from P to N limitation in an average year. Model parameters controlling the delivery of N and P by the environment and the biological utilization of nutrients by the phytoplankton were drawn from random distributions based on literature reports or, where available, data from the Rhode River. Model output for each parameter set was classified according to which, if any, of the classes of bloom it exhibited. Environmental processes most responsible for the variability in predicted spring blooms were the rate of phosphorus release from the sediment, the timing of nitrate depletion at the seaward boundary, and the maximal nitrate concentration at the boundary. Simulation of bloom failure was most strongly associated with low rates of phosphorus release from the sediment. Phytoplankton physiological parameters most responsible for variability in categories of behavior were the nitrogen:chlorophyll conversion factor, and the maximum internal storage capacity for phosphorus. Blooms of extraordinary magnitude were associated with low nitrogen:chlorophyll ratios and high storage capacity for phosphorus. Results help identify key processes and parameters in need of further understanding as well as possible points for managerial intervention. Phytoplankton · Spring bloom · Estuarine · Nitrogen · Phosphorus Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 154. Publication date: July 31, 1997 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1997 Inter-Research.

Longwaves and primary productivity variations in the equatorial pacific at 0°, 140dgW

High temporal resolution measurements of physical and bio-optical variables were made in the upper ocean using a mooring located at 0°, 140°W from 9 February 1992 to 15 March 1993 as part of the equatorial Pacific Ocean (EgPac) study. Chlorophyll and primary productivity time-series records were generated using the mooring data. Primary productivity varied by about 50% around the mean on time scales of weeks and by over a factor of four within our observational period. The mooring observations encompassed both El Niho and cool conditions. Kelvin waves were evident during the El Nifio phase, and tropical instability waves (TIWs) were dominant during the cool phase. The two extreme conditions also were observed concurrently with complementary ship-based measurements. In addition, bio-optical drifters provided simultaneous spatial data concerning net phytoplankton growth rates during passage of a TIW. The collective data sets have been used to examine the causes of the observed variability in phytoplankton biomass and productivity. Our joint results and analyses appear to support the hypothesis that the vertical transport of iron into the upper layer and primary production rates are modulated by variability of the depth of the Equatorial Undercurrent and by equatorial longwaves. In particular, our results are consonant with the suggestion of Barber et al. (1996) that passage of a TIW may be considered to be a natural analog of a small iron enrichment experiment. Predicting primary productivity and, thus, carbon flux in the equatorial Pacific requires continuous, long-term observations of a few physical, biological, and optical properties that can be used to parameterize the biological variability.

Using non-linear analysis to compare the spatial structure of chlorophyll with passive tracers

A form of non-linear analysis, termed the near-neighbour algorithm, was applied to transects of chlorophyll and salinity collected off eastern Antarctica in the Austral summer of 1995/96. The near-neighbour algorithm was initially developed to detect chaos in time series, but was applied here to compare the spatial structure of chlorophyll, a non-conservative tracer, with that of a conservative tracer, salinity. The validity of such an application is discussed in the context of the literature and as a complementary approach to traditional methods such as autocorrelation and spectral analysis. The results indicate that the spatial structure of salinity could be classified as non-linear in nature. The structure of chlorophyll at corresponding spatial scales contains a stochastic component, and it is postulated that this is caused by biological factors, specifically net phytoplankton growth. The potential for expanded, more detailed analyses is discussed, and parallels are drawn between the current state of non-linear analysis in biological oceanography and the development of spectral analysis over the last three decades.

Preliminary investigation of the contribution of fast-ice algae to the spring phytoplankton bloom in Ellis Fjord, eastern Antarctica

Algae released from fast-ice in Ellis Fjord, eastern Antarctica, made little contribution to subsequent phytoplankton growth. Dominant taxa in the interior ice community included Nitzschia cylindrus (Grun) Hasle, Navicula glaciei V.H. and a dinoflagellate cyst. Diatom mortality within the ice was high. The algal contribution to the phytoplankton from the fast ice was estimated by calculating the difference between algal biomass in ice cores taken on 14 November with those taken on 18 December 1992. The biomass of sedimenting phytoplankton was estimated using sediment traps; weekly cell counts of water were used to monitor net phytoplankton growth. The low contribution from the fast-ice of Ellis Fjord to the phytoplankton is similar to results from other Antarctic fast-ice communities but is not necessarily reflective of processes occurring within either Antarctic or Arctic pack ice communities. An algal mat growing on the base of the fast-ice had a carbon standing crop of between 0.231 gC m-2 and 0.022 gC m-2. Much of this was delivered to the water column as the ice melted while the remainder was exported.

Development and Testing of a Nitrogen Model for Onondaga Lake

ABSTRACT A dynamic two-layer mass balance model for total nitrogen (N) and various species of N is developed and tested for Onondaga Lake, NY, a system in which high concentrations of total ammonia (T-NH3) prevail. The model simulates concentrations of T-NH3, nitrate plus nitrite, particulate organic N (PON), dissolved organic N, total Kjeldahl N, and total N. Processes of the N cycle accommodated include net phytoplankton growth, nitrification, denitrification, ammonification, decay of PON, volatilization of free ammonia, sediment release of T-NH3, settling of PON, and vertical mixing-based exchange between the layers. Model testing is supported by a comprehensive monitoring database of lake concentrations of the N species, and tributary and waste discharge concentrations for calculation of loads. Model credibility is enhanced by the independent determination of several important model coefficients based on field and laboratory experiments, which greatly reduces the role of calibration. Model verificatio...

Modelling impact of urban and upstream nonpoint sources on eutrophication of the Milwaukee River

This paper describes a study conducted to evaluate the impact of the absence vs. the presence of the North Avenue Damin Milwaukee, Wisconsin, on water quality in the Milwaukee River in terms of conventional constituents, such as DO, chlorophyll a, BOD, and nutrients (N and P). Phytoplanktonic primary production had been recognized earlier as a link between mostly nonpoint nutrient loads to the Milwaukee River and degradation of water quality in the River. A mathematical model of a relevant section of the River was used in the study to estimate the effect of the removal of the Dam on this primary production link. The authors established the model using WASP, which is USEPA's widely used modelling package. The modelled extent of the River included both shallow, productive upstream reaches as well as impounded downstream sections. In the impounded reach of the River where the Dam is located, the simulated removal of the Dam (1) replaced net phytoplankton decay with net phytoplankton growth because of improved light conditions and limited settling; (2) substantially increased the concentration of DO because of the increased photosynthetic production and reduced benthic consumption; and (3) somewhat increased bottle BOD5 because of the elevated phytoplankton levels. The simulated removal of the Dam eliminated the negative effects of eutrophication at the site while possibly shifting the potential for these effects further downstream towards Lake Michigan.

Modelling impact of urban and upstream nonpoint sources on eutrophicationof the Milwaukee River

This paper describes a study conducted to evaluate the impact of the absence vs. the presence of the North Avenue Damin Milwaukee, Wisconsin, on water quality in the Milwaukee River in terms of conventional constituents, such as DO, chlorophyll a, BOD, and nutrients (N and P). Phytoplanktonic primary production had been recognized earlier as a link between mostly nonpoint nutrient loads to the Milwaukee River and degradation of water quality in the River. A mathematical model of a relevant section of the River was used in the study to estimate the effect of the removal of the Dam on this primary production link. The authors established the model using WASP, which is USEPA's widely used modelling package. The modelled extent of the River included both shallow, productive upstream reaches as well as impounded downstream sections. In the impounded reach of the River where the Dam is located, the simulated removal of the Dam (1) replaced net phytoplankton decay with net phytoplankton growth because of improved light conditions and limited settling; (2) substantially increased the concentration of DO because of the increased photosynthetic production and reduced benthic consumption; and (3) somewhat increased bottle BODS because of the elevated phytoplankton levels. The simulated removal of the Dam eliminated the negative effects of eutrophication at the site while possibly shifting the potential for these effects further downstream towards Lake Michigan.

On the net growth of phytoplankton in two dutch estuaries

Langdon's model has been used in the calculation of net primary production of phytoplankton in the (turbid, eutrophic) Westerschelde and (relatively transparent) Oosterschelde estuaries. The results for the Westerschelde are shown to be much closer to the observed values than is achieved using other methods (fixed respiration rate) of calculation.

On the net growth of phytoplankton in two Dutch estuaries

Langdon's model has been used in the calculation of net primary production of phytoplankton in the (turbid, eutrophic) Westerschelde and (relatively transparent) Oosterschelde estuaries. The results for the Westerschelde are shown to be much closer to the observed values than is achieved using other methods (fixed respiration rate) of calculation.