Nutrient Trapping Research Articles

Consequences of winter upwelling events on biogeochemical and phytoplankton patterns in a western Galician ria (NW Iberian peninsula)

The consequences of two upwelling events in mid- (MW) and late (LW) winter on biogeochemical and phytoplankton patterns were studied in the Pontevedra Ria and compared with the patterns measured under typical winter conditions and under a summer upwelling event. Thermohaline patterns measured during the mid-winter upwelling event (MW-up) revealed the intrusion of saltier seawater (35.9) into the ria associated with the Iberian Poleward Current (IPC). During the late-winter upwelling event (LW-up), the seawater which had welled up into the ria showed characteristics of the Eastern North Atlantic Central Water mass (ENACW). In both cases the measured water residence time (4 days during MW-up and 10 days during LW-up) was related to both meteorological and fluvial forcing. This residence time contrasts with that of summer upwelling (7 days) and with that estimated under unfavorable upwelling atmospheric conditions (2–4 weeks). During MW-up, the ria became poor in nutrients due to continental freshwater dilution, associated with the shorter residence time of the water, and the intrusion of IPC, which is a water body poor in nutrient salts: 2.9 μM of nitrate, 0.1 μM of phosphate and 1.5 μM of silicate. During this event, the ria exported 3.4 mol DIN s −1, compared with 6.9 mol DIN s −1 in non-upwelling conditions. Phytoplankton showed a uniform distribution throughout the ria, as during unfavorable upwelling conditions, and was characterized by the dominance of diatoms, mainly Nitzschia longissima and Skeletonema costatum. During LW-up, a nutrient depletion in the photic layer also occurred, but as a result of a phytoplankton spring bloom developing at this time. The ria was a nutrient trap where 4.1 mol DIN s −1 were processed by photosynthesis. This budget is three times higher than the one under non-upwelling conditions. In contrast with the MW-up, which had no effect on primary production, during LW-up the ria became more productive, although not as productive as during a summer upwelling event (9.9 mol DIN s −1). The taxonomic composition of the phytoplankton community did not change noticeably during LW-up and the summer upwelling, with the same species present and changing only in relative proportions. Diatoms were always the dominant microphytoplankton community, with Pseudonitzschia pungens, Thalassionema nitzschioides and several species of Chaetoceros as characteristic taxons.

Optimization and sensitivity study of a biogeochemistry ocean model using an implicit solver and in situ phosphate data

A new implicit method for obtaining equilibrium solutions and their sensitivity to changes in parameters is described and applied to an OCMIP‐2 type ocean‐biogeochemistry model. The method is used to optimize model parameters by minimizing the difference between the observed and simulated PO4 distribution. The optimized parameters include (1) the exponent α in the power law vertical profile for particulate organic matter (POM) fluxes, (2) the fraction σ of biological production allocated to dissolved organic matter (DOM) and (3) the rate constant κ for the remineralization of DOM. Global PO4 observations constrain σ and κ but not independently because their sensitivity patterns are highly correlated. In contrast, the sensitivity pattern for α is uncorrelated to those of the other parameters, allowing it to be independently constrained. We show that export production from POC is well constrained by the distribution of PO4 in an OCMIP‐2 type model, but that new production and export production from DOC are not well constrained. With the optimal parameter set (α = −1.0, σ = 0.74, and κ = 1.0 yrs−1) the fraction of the spatial PO4 variance captured by our model increases from 60% with the reference OCMIP‐2 parameters to 70%. Combined changes in σ and κ account for most of the improvements by reducing but not completely eliminating the nutrient trapping effect in the Eastern Equatorial Pacific and northern Indian Ocean that causes the model to over‐predict PO4 concentrations. Important remaining model‐data misfits in the deep North Atlantic where PO4 is over predicted and in the North Pacific where the model does not produce the observed sharp nutricline are likely attributable to deficiencies in ocean transport. The fact that the fraction of unexplained variance is large at the optimal parameter values highlights the importance of properly simulating physical transport for ocean biogeochemical modeling.

Going against the flow: Effects of river damming in Cuban fisheries

Over the last decade eutrophication of freshwater artificial reservoirs in Cuba occurred in parallel to oligotrophication of estuarine and coastal waters. These two processes influenced both freshwater and marine fisheries. A dramatic shift in species composition in freshwater fisheries has occurred, from dominance by cichlids (tilapia) to dominance by cyprinids. The high fishery yield from some reservoirs, and shift in species composition, seems related to progressive eutrophication of reservoirs by nutrient subsidies from different anthropogenic activities; particular those related to the size of urban areas within their watersheds. On the other hand, marine landings of estuarine-dependent species declined more significantly than for other groups associated with seagrass beds–coral reefs and oceanic waters. The ratio between catches of estuarine-dependent species and those associated with seagrass beds and coral reefs, decreased significantly over the last 20 years. The decrease in landings was more evident in typical estuarine species, such as shrimps ( Litopenaeus schmitti and Farfantopenaeus notialis), mangrove oyster ( Crassostrea rhizophorae) and mullets ( Mugil spp.). River damming increased during the same period and is significantly correlated with these decreases. It is hypothesized that two different processes acted synergistically, leading to dramatic decreases of several orders of magnitude, in the catches of estuarine species over the last decade: the trapping of nutrients and sediments by river damming, and a drastic reduction in nutrient inputs from land-based sources due to reduced fertilizer use. These are postulated to have affected not only estuarine resources, but also the whole coastal ecosystem.

Cuticular discontinuities in glandular hairs of Genlisea St.-Hil. in relation to their functions

The terminal cells of glandular hairs are shown to be the only permeable sites on the trap surface. A cuticle of these cells of internal hairs forms pores. These discontinuities can be demonstrated directly by SEM and indirectly by using a vital stain. Cuticular discontinuities of internal trap hairs are involved in the discharge of hydrolytic enzymes and the absorption of the products of the digestion (internal trap nutrients absorption). For external trap hairs was suggested that they are hydropoten and play a role in both water and ions transport (external trap nutrients and water absorption). In some Genlisea species, sessile hairs on the underground parts may play a role in water transpiration. In other species like Genlisea filiformis and G. aurea, these hairs produce mucilage which is a habitat of the community of microorganisms.

Nutrients in the gully, Scotian shelf, Canada

The Gully is a large shelf‐edge submarine canyon located on the eastern Scotian Shelf which has long been recognized as an area rich in marine life. This paper analyses the available nutrient (nitrate, silicate and phosphate) data for The Gully, including the new information collected since The Gully was designated a potential Marine Protected Area in 1998, and reports on nutrient climatology, nutrient transports and transport mechanisms, and surface nutrient distributions with a focus on how nutrient behaviour may or may not be different in The Gully than observed elsewhere on the Scotian Shelf. Seasonal cycles for nutrients in The Gully show the general patterns expected for nutrients in temperate coastal waters. The concentrations of all three nutrients in the surface layer (z ≤ 50 m) are relatively high in late fall and winter. Nitrate and silicate levels fall rapidly during the spring bloom and remain low during the summer and fall. Nitrate is more severely depleted than silicate. Phosphate levels are also lower in summer than in winter, but not depleted in summer, which is consistent with a nitrogen limited ecosystem. Attenuated versions of these seasonal cycles for the three nutrients are evident in the intermediate layer (50 < z ≤ 100 m), with substantial quantities of nutrients remaining in the summer. Little evidence of a seasonal cycle is seen in deeper waters (z > 100 m). These nutrient concentrations and seasonal cycles are similar to those found elsewhere on the shelf. A more detailed examination of nutrient concentrations in The Gully shows that higher nitrate, silicate and phosphate levels occur at the head of The Gully compared to the mouth, and on the Sable Bank side of The Gully compared to the Banquereau side. These observations are consistent with a trapping of nutrients associated with the counter‐clockwise circulation within The Gully, which could fuel more primary productivity in The Gully than on the adjacent shelf. Nutrient levels determined from surface samples collected at high frequency while survey vessels were underway showed anomalously high surface concentrations of nitrate and silicate that were consistent with the areas where the interaction of gully currents with the bottom topography at the head of The Gully and breaking internal waves along the north‐east edge of The Gully would enhance vertical mixing. Calculations of transports of nutrients through The Gully show that ∼5% of the external inputs of nitrate to the eastern Scotian Shelf are supplied through The Gully in winter, and ∼25% flow through The Gully in summer. Calculations based on these physical processes and the observed nutrient levels show that such mechanisms have the potential to increase production substantially in The Gully compared to other areas of the shelf.

Seasonal ecological changes and water level variations in the Sélingué Reservoir (Mali, West Africa)

This work investigates the ecological modifications induced by the annual water level change as a consequence of hydrological regime and power production in Sélingué, a monomictic reservoir in Mali (West Africa). High waters occur from November, after the flood, while low waters occur from June, at the end of the dry season. Decrease of water level is linked to environmental factors (marked hydrological pattern, both for river flow and rain) and to human management of the reservoir during the dry season (irrigation, high hydropower demand). Difference in elevation between the high water and the low water phases is 9 m. To assess the ecological impact of such water level variations, environmental and biological descriptors were studied on water sampled biweekly from November 2000 to November 2001 in stations representative of the north part of this water body. As a consequence of high water and of regional meteorology (NE trade winds), the water column in Sélingué is stratified from March to May. Stratification can act as a trap for nutrients in the hypolimnion, preventing the euphotic epilimnion to be realimented in dissolved P and N mineral components. This process lasts until the beginning of the monsoon (SW trade winds) when progressive warming and energetic inputs through storms allow vertical mixing. The sink-phase is then replaced by a spring-phase when the water column is not anymore stratified and when the water level is low enough to allow wind-induced resuspension and vertical mixing. At the end of the low water phase, phytoplankton blooms are observed, allowed by the proximity of the productive euphotic layer and the deep mineralization layer and their possible mixing. Water level is also important for fisheries, since fishes are “diluted” in high water (i.e., more difficult to catch with the artisanal tools operated by the local fishermen) but are “concentrated” in low water (i.e., more easily over fished in the minor riverbed, where most fishes are sheltered at the end of the dry season). Irrigation was until now a secondary purpose of the Sélingué project, behind power production. Sélingué is now of secondary importance for power production in Mali (behind Manantali) and the planned extension of irrigated areas in the Office du Niger is about to seriously increase the need of water from Sélingué, the only impoundment upstream. During a hydrological cycle, the only conditions possibly leading to ecological unbalance are met at the end of the low water period. As long as the water level is high enough to allow vertical stratification and vertical separation of the productive euphotic layer from the sink in the bottom layer, Sélingué trophic status varies from oligotrophy to mesotrophy. The low water phase is very sensitive, and wise management rules should limit its duration. But the projects leading to a more intensive and time-shifted use of Sélingué water could have as consequences an early dewatering of the reservoir and an early shift toward eutrophic conditions. Therefore, there is a need to define and to apply multipurpose rules of water level management that could help to minimize or to prevent these ecological consequences.

Grass Barriers for Reduced Concentrated Flow Induced Soil and Nutrient Loss

Vegetative filter strips (FS) perform poorly for reducing losses of sediment and nutrients in concentrated flow. Stiff‐stemmed grass barriers (B‐FS) above the FS may be a companion treatment to improve the FS performance. This study evaluated the effectiveness of warm‐season switchgrass (Panicum virgatum L.) barriers planted above fescue (Festuca arundinacea Schreb.) FS in reducing runoff water, sediment, N, and P losses in concentrated flow from an Aeric Vertic Epiaqualf on a 5% slope. Simulated rainfall was applied on plots consisting of a 1.5‐m‐wide by 8‐m‐long pollutant source area with an artificially constructed channel to concentrate surface runoff. The source area was bounded downslope by either an 8‐m long fescue FS or 0.7 m of active or dormant barrier above a 7.3‐m‐long fescue FS. The B‐FS treatment also reduced sediment loss by 91% while the FS reduced sediment by only 72% (P &lt; 0.01). The B‐FS also reduced sediment loss by 90%, whereas FS reduced sediment only 60% when inflow was added to the plots. The B‐FS trapped 4.9 times more organic N, 2.3 times more NH4–N, and 3.7 times more particulate P than FS at 0.7 m (P &lt; 0.01). Sediment and nutrient trapping increased significantly with FS length. Switchgrass barriers above the FS dispersed and temporarily ponded concentrated runoff, enabling increased sediment deposition. Barriers may be a potential conservation strategy for rehabilitation of lands affected with concentrated flow where traditional practices are inadequate.

Biogeochemical cycles during the species succession from Skeletonema costatum to Alexandrium tamarense in northern Hiroshima Bay

Temporal variations, budgets and cycling patterns of major biophilic elements [phosphorus (P), nitrogen (N) and silicon (Si)] in northern Hiroshima Bay during species succession from Skeletonema costatum to Alexandrium tamarense were documented using data collected on a weekly basis in 1996 and 1997. The budget calculations using a box model were made from the perspective of both particulate formation and decomposition of particulate matter. Thus, the overall circulation patterns of these three elements and their differences were examined in the present study. The turnover time of P was longer than that of N, indicating that the utilization efficiency of P by organisms is low. Along with this, absolute concentrations of dissolved inorganic phosphorus in this season and elemental ratios calculated from various forms of biophilic elements support the idea that DIP is too low for phytoplankton to utilize it. However, the utilization efficiency of P was higher in 1997 than in 1996, when A. tamarense formed a more intensive bloom, suggesting that these organisms could retain elements. When the bloom of A. tamarense formed in 1997, the residence time of water was extremely long, indicating that stagnation of water is a primary factor for bloom formation. In contrast to the large fluctuation in the residence time of water, residence times of biophilic elements were almost constant, indicating the importance of biological processes occurring in the system. On the other hand, in 1996, the residence times of biophilic elements were usually longer compared to that of water. This suggests that the particulate formation process by phytoplankton acts as a “nutrient trap” in combination with estuarine circulation.

Circulation and zooplankton biomass distribution over the southern Patagonian shelf during late summer

In this article we use hydrographic data collected in the period 1994–2000 to analyze the summer distributions of temperature and salinity in the southern Patagonian shelf (Argentina). The objective is to infer the circulation patterns of the Patagonian shelf and to relate them to the zooplankton biomass distribution. The vertical structure of the hydrographic variables indicates the existence of two distinct regions. North of 51°S, the water column can be characterized as a two-layer system separated by a thermocline at approximately 50 m depth. South of 51°S, the density structure of the water column is nearly homogeneous. The two regions are separated by a front that extends in a northeast direction from the coastal region of the Grande Bay towards the continental slope. The circulation patterns inferred from the observed fields indicates that although the circulation in the southernmost portion of the Patagonian shelf, i.e., from Tierra del Fuego to the Grande Bay front, is towards the north, as predicted by previous studies, this northward flow turns offshore at the location of the Grande Bay front. This frontal region and the associated circulation pattern have not been previously described. The inferred circulation may enhance zooplankton production and accumulation over the coastal area of the Grande Bay—via increased primary production, by favoring both the enrichment and trapping of nutrients, and the retention of organisms.

Nutrient concentrations in the Middle Parana River: effect of the floodplain lakes

Water composition and sediment calcium, iron, aluminium and phosphorus fractions were determined monthly during one year in the Middle Parana River, a floodplain lake in permanent contact with it and a representative affluent, the San Javier River. The same measurements were made in the Parana main stem and in five floodplain lakes along 400 km of the Middle Parana stretch in coincidence with a flood and the subsequent low water phase. During the flood, soluble reactive phosphorus (SRP) and nitrate decreased downstream along the river. The lakes showed generally higher transparency, conductivity and major ion concentration and lower pH, oxygen, nitrate, SRP and iron than the river. Bottom sediments were mainly composed of sand in the river and clay in the lakes. Consequently, the lake sediments showed higher iron, aluminium, calcium and TP content. The river sediments contained higher amounts of the residual P fraction and roughly the same amount of iron and calcium bound P while the lakes showed an enriched iron bound P together with impoverished calcium and residual P fractions. Improved transparency within the lakes indicated suspended matter settlement within them. Riverine-contributed nitrate and SRP sustained the high macrophytic productivity in the lakes. Decomposition of the litter produced by the macrophytes caused lower oxygen concentrations and pH in the lakes than in the incoming river water. Denitrification in the water-sediment surface is suggested to be an important N sink. Coprecipitation of SRP with iron and suspended matter is likely contributing to the lower SRP concentration in the lake water. Transformation of calcium bound P from the incoming river sediments into iron bound P within the lakes sediments is a major process contributing to the high SRP retention within the lakes. It is concluded that the floodplain lakes represent a long-term trap for nutrients partially counteracting upstream cultural enrichment and improving eutrophication-related water quality in the river.

Sedimentology and geochemistry of an urban coastal lake system: Coombabah Lake Nature Reserve, Gold Coast, Queensland

A study was initiated to address environmental concerns associated with changes in land use in the catchment area of Coombabah Lake, a brackish coastal lake system located in southeast Queensland. Sedimentological and geochemical data derived from a series of cores that penetrate the ca. 0–6000 year‐old lacustrine sequence indicate that throughout much of its history, Coombabah Lake has remained a quiet, shallow, water body fed by fine‐grained sediment dropped from suspension. Discrete and laterally continuous, shelly horizons form the basis for the stratigraphy developed for the lake sequence. A lithological transition in the upper 50 cm of the sediment column, from mud to shell‐rich, sandy mud, suggests that the depositional regime changed ∼500 years ago as accommodation space was filled. At this time, the dominant sedimentary processes changed to include reworking, partial bypass of sediment, the intermittent concentration of shell debris by winnowing, and the development of a flood‐tidal delta complex in the lower reaches of the lake. Sharp increases in total organic carbon, total nitrogen, and total phosphorus concentrations below the lithological transition at 50 cm depth suggest that the capacity of the system to preserve organic matter and trap nutrients decreased significantly after the transition in depositional regime. Results indicate that current conditions in Lake Coombabah are governed by natural processes associated with the long‐term evolution of coastal lake systems, and reveal little to suggest that there were any adverse affects resulting from recent human activities in the surrounding catchment.

Nutrient removal from farm effluents

The objectives of the study were: (i) to examine the efficiency of nutrient removal during the treatment of dairy farm effluent in a two-pond system, and (ii) to produce an inexpensive but effective nutrient trap which could be recycled as a nutrient source or soil mulch. The concentration of chemical oxygen demand (COD), biological oxygen demand (BOD), nitrogen (N), phosphorus (P) and potassium (K) in a two-pond system used to treat dairy farm effluent was monitored over a period of 7 months. The retention of nutrients by two porous materials was examined both in the laboratory batch (zeolite and bark) and pilot-scale field (bark) experiments. The results indicated that biological treatment of farm effluents using the two-pond system was not effective in the removal of nutrients, which are likely to become pollutant when discharged to waterways. Both the bark and zeolite materials were effective in the removal of N, P and K from effluent. These materials can be placed in the second (i.e., aerobic) pond to treat effluents, which can then be discharged to streams with minimum impact on water quality. The nutrient-enriched porous materials can be recycled as a source of nutrients and soil conditioner.

Erosion-related soil carbon fluxes in a pastoral steepland catchment, New Zealand

Abstract New Zealand is currently identifying and quantifying its carbon sources and sinks to develop a national carbon budget. This will enable it to set policy and targets to reduce greenhouse gas emissions in line with the Kyoto Protocol. While soil is a major carbon sink, New Zealand also has high sediment yields to the ocean, suggesting that erosion has a significant effect on soil carbon fluxes, through CO2 emission during transport of carbon in sediment, carbon burial and recovery of carbon on eroded areas. As a contribution to the national carbon budget, a mass balance approach was used to calculate soil carbon fluxes from landslide and sheetwash erosion in the Tutira catchment in the North Island of New Zealand. This soft rock hill country catchment represents the upper limit for landslide-related soil carbon losses. It contains a lake that acts as a highly efficient trap for sediment and nutrients, and has preserved a high-resolution record of storm-induced erosion. Information from previous studies of erosion and lake sedimentation was used to construct a carbon budget for the 114-year period of European pastoral farming. The budget assumes the gross transfer of carbon by geomorphological processes and does not include biogeochemical exchanges with the atmosphere. Results indicate that 0.94±0.23 Mg C ha−1 per year enter the lake (0.50±0.15 Mg C ha−1 per year from landslide erosion and 0.44±0.17 Mg C ha−1 per year from sheetwash erosion). On a national scale this equates to an anthropogenically induced loss of 2 112 000 Mg C per year from the 10% of similar terrain under pastoral land use. However, the net loss from the landscape is significantly less due to carbon recovery on eroded sites. Landslide scars have a carbon recovery rate (after oxidation) of ∼0.61 Mg C ha−1 per year. Carbon recovery on areas affected solely by sheetwash erosion was not measured, but is significantly lower. This information is being used to constrain models of erosion-related carbon fluxes developed for landslide-prone terrains, as part of the national carbon budget.

Water and sediment quality, partial mass budget and effluent N loading in coastal brackishwater shrimp farms in Bangladesh

The present study aimed to quantify the water and sediment quality and growth and production parameters and to establish nutrient budgets for an average of five selected semi-intensive shrimp ponds in Bangladesh over a growing cycle. Physico-chemical parameters of water and sediments were measured and analyzed by standard methods. Gross yield (kg ha −1) of shrimp was calculated from the stocking and harvesting data. Finally, a partial nutrient mass budget for N and P was calculated. Most of the parameters of water and sediments correlated significantly with each other suggesting a high degree of interactions between different parameters in the system. Significantly higher concentrations of all species of nitrogenous nutrients were recorded in the effluent waters than that entering into the ponds. Therefore, a high loading and net output of nitrogenous nutrients in effluent waters was documented. The study also indicated a net discharge of solids and minerals through effluent loading. However, significantly lower concentrations of phosphorus in the effluent water indicated a net retention and trapping of phosphatic nutrients in the environment. Total production ranged between 532.0 and 697.0 kg ha −1 cycle −1 and P. monodon production between 484.0 and 562.0 kg ha −1 cycle −1. Ponds gained nitrogen primarily from intake water (55%) and fertilizers (29%), and nitrogen was lost primarily from water exchange (78%) and harvested shrimp (12%). Phosphorus gain occurred mostly from intake water (52%) and fertilizers (25%), and phosphorus was lost primarily from water exchange (52%) and harvested shrimp (3.3%). About 10% of input nitrogen and 44% of phosphorus were not accounted for in measured losses, and presumably were fixed or metabolized in the system. On average, 78 g N was discharged to and 25 g P was removed from the surrounding water by the system for each kilogram of shrimp produced. Mean conversion of feed nitrogen and phosphorus to shrimp flesh averaged 74% and 40%, respectively. It was concluded that semi-intensive systems serve as net supplier of N to and net remover of P from the surrounding water.

Evaluating mechanisms of nutrient depletion and 13C enrichment in the intermediate‐depth Atlantic during the last ice age

Using an ocean box model, we have studied the effect of altered circulation on the oceanic distributions of phosphate (PO4−3) and the 13C/12C and 14C/12C of dissolved inorganic carbon to evaluate competing hypotheses for the cause of observed nutrient depletion and 13C enrichment at intermediate depths of the Atlantic during the last ice age. Because of “nutrient trapping” and limited air‐sea carbon isotopic equilibration, the simple imposition of an intense meridional overturning cell in the Atlantic fails to simultaneously lower nutrient concentrations and raise 13C/12C to observed glacial levels. Export of intermediate water out of the Atlantic causes a basin‐to‐basin nutrient transfer, thus providing a more efficient mechanism of intermediate‐depth Atlantic nutrient depletion and improved carbon isotopic equilibration at low temperatures (i.e., 13C enrichment). Although this export adds nutrients to the intermediate depths of the Pacific and Indian Oceans, the simulated glacial intermediate‐depth Indo‐Pacific is nevertheless moderately depleted in PO4−3 relative to the model's interglacial control, in agreement with consensus paleoceanographic evidence. This Indo‐Pacific PO4−3 depletion results from our use of a “glacial base case” in which nutrient‐rich Antarctic Intermediate Water formation is absent as part of the elimination of the modern North‐Atlantic‐Deep‐Water‐based “conveyor” circulation.

WATERSHED WEIGHTING OF EXPORT COEFFICIENTS TO MAP CRITICAL PHOSPHOROUS LOADING AREAS1

ABSTRACT: The Export Coefficient model (ECM) is capable of generating reasonable estimates of annual phosphorous loading simply from a watershed's land cover data and export coefficient values (ECVs). In its current form, the ECM assumes that ECVs are homogeneous within each land cover type, yet basic nutrient runoff and hydrological theory suggests that runoff rates have spatial patterns controlled by loading and filtering along the flow paths from the upslope contributing area and downslope dispersal area. Using a geographic information system (GIS) raster, or pixel, modeling format, these contributing area and dispersal area (CADA) controls were derived from the perspective of each individual watershed pixel to weight the otherwise homogeneous ECVs for phosphorous. Although the CADA‐ECM predicts export coefficient spatial variation for a single land use type, the lumped basin load is unaffected by weighting. After CADA weighting, a map of the new ECVs addressed the three fundamental criteria for targeting critical pollutant loading areas: (1) the presence of the pollutant, (2) the likelihood for runoff to carry the pollutant offsite, and (3) the likelihood that buffers will trap nutrients prior to their runoff into the receiving water body. These spatially distributed maps of the most important pollutant management areas were used within New York's West Branch Delaware River watershed to demonstrate how the CADA‐ECM could be applied in targeting phosphorous critical loading areas.

Geochemical evidence of denitrification in the Benguela upwelling system

This paper presents analysis of nitrate, phosphate and silicate data from the Benguela upwelling system. Evidence is presented that suggests denitrification occurring close to shore, and also nutrient trapping. Denitrification leaves an imprint on the water properties in terms of a nitrate deficit, that is to say nitrate concentrations that are significantly less than predicted by multiplying the phosphate concentrations by the Redfield ratio. It is probable that denitrification also causes a decoupling of nitrate and carbon compared to Redfield processes, and large-scale losses of nitrate in the Benguela which are not accompanied by losses of carbon. Nitrate-driven CO 2 drawdown following upwelling will be less than it might otherwise be, because of denitrification. Nutrient trapping (secondary remineralisation) is apparent as enhanced phosphate concentrations, some of which are several μmol higher than in the offshore source waters for upwelling. Waters also become enriched in silicate and to a lesser extent nitrate as they advect across the shelf. By implication the same process should also “supercharge” waters in dissolved inorganic carbon, leading to stronger outgassing of CO 2 immediately after upwelling. The effect is again to increase the size of the estimated Benguela upwelling system CO 2 source.

Regional scale variability in sediment and nutrient delivery from small agricultural watersheds.

Although many studies have pointed out the various controlling factors of sediment and nutrient delivery on a plot or watershed scale, little is known on the spatial variability of sediment and nutrient delivery on a regional scale. This study was conducted to reveal regional variations in sediment-associated nutrient delivery in central Belgium. Sediment deposited in 13 small retention ponds was sampled and analyzed for total phosphorus (TP), K, Mg, and Ca content. The TP content of the sediment deposits varied from 510 to 2001 mg P per kg sediment. Nutrients are predominantly fixed on the very fine sediment fraction (<16 microm), which is the reason why the nutrient trap efficiency of the ponds is only a fraction of the sediment trap efficiency. Average nutrient trap efficiency of the studied ponds varies between 4 and 31%, whereas sediment trap efficiency varies between 10 and 72%. For watersheds ranging from 7 to 4873 ha, sediment yield ranged between 1.2 and 20.6 Mg ha(-1) yr(-1), whereas TP export varied from 1.8 to 39.7 kg ha(-1) yr(-1). The observed spatial variability in nutrient losses is primarily attributed to regional variations in erosion and sediment yield values and to a far lesser degree to the spatial variations in fertilizer application. Redistribution of manure in the framework of an agricultural policy may increase the rate of nutrient delivery by ways of erosion and sediment transport.

Application of the Two-Dimensional Hydrothermal and Water Quality Model, CE-QUAL-W2, to the Chesapeake Bay – Conowingo Reservoir

ABSTRACT The application of the two-dimensional hydrothermal and water quality model, CE-QUAL-W2, to the Conowingo Reservoir is presented. The performance of the CE-QUAL-W2 model was enhanced with the addition of multiple particle size settling rates, and an algorithm to account for the scour process within a reservoir. The benefit of the Conowingo Reservoir to perform sediment and nutrient trapping was determined from the calculation of removal efficiencies which showed important characteristics for this reservoir which is near the end of its useful lifespan in regards to trapping capability.

Diffusion with evolving sources and competing sinks: development of angiogenesis.

Tumors ensure their long-time growth by emitting molecular messengers that induce cellular modifications in neighboring capillaries. These modifications are conducive to the enlargement of the vascular system feeding the tumor. This phenomenon, termed angiogenesis, is controlled by the diffusion and competitive trapping of nutrients and molecular messengers by several cell species. The number, location, and properties of these traps change continuously. The angiogenic process also implies that nutrient sources are time dependent. Starting from assumptions at the cellular level, we formulate a mathematical model that predicts the evolution of angiogenesis and the increase in the blood flow to the tumor. The model also predicts the emergence of directed growth and the possibility of therapeutical synergy. Simulations permit a careful analysis of the influence of the main parameters.