Total Phosphorus Input Research Articles

Phosphorus Inputs to Lake Simcoe from 1990 to 2003: Declines in Tributary Loads and Observations on Lake Water Quality

Total phosphorus (TP) inputs to Lake Simcoe have led to hypolimnetic dissolved oxygen (DO) depletion and loss of cold water fish habitat. Since 1990, efforts have been made to reduce the total TP input to the lake below a defined target of 75 t/year, which was predicted to lead to reductions in spring TP concentration and improvements in end-of-summer hypolimnetic DO concentrations. The total TP load to the lake during the most recent period of record (1998/99-2003/04) ranged from 53 to 76 t/yr and averaged 67 t/yr, compared to an average of 114 t/yr estimated between 1990/91 and 1997/98 (range 85-157 t/yr). Reductions in TP loads from the catchment via tributary discharge (∼26 t) accounted for the majority of the decrease in total load between the two time periods. Total P concentrations decreased significantly in four out of six long-term monitored tributaries; however, concentrations in all six tributaries remain above the level recommended to avoid nuisance plant growth (30 μg/L). Although TP loads to the lake are currently below the target 75 t/yr, excessive growths of filamentous algae and macrophytes continue to be a problem in the nearshore zone. End-of-summer minimum hypolimnetic DO concentrations (average 4.3 mg/L, 1998/99-2003/04) remain substantially below the level (7 mg/L) that is considered protective of lake trout. Efforts to reduce TP loads to the lake therefore need to continue.

Seasonal and regional variations in precipitation chemistry in the Lake Taihu Basin, China

To evaluate seasonal and regional variations in precipitation chemistry in Lake Taihu Basin, 5 cities around the lake were selected for monthly collection of rainfall samples from July 2002 to June 2003. The analytical parameters included pH, cations (K +, Na +, Ca 2+, Mg 2+, NH 4 + ), anions (F −, Cl −, SO 4 2 - , NO 3 - ), total nitrogen (TN) and total phosphorus (TP). In descending order, concentrations (in meq L −1) of the ions in wet deposition can be ordered as SO 4 2 - > Ca 2 + > NH 4 + > NO 3 - >Cl −>Na +>Mg 2+>K +>F − with concentratin percentages of 48.7%, 19.1%, 11.6%, 8.1%, 5.6%, 2.6%, 1.7%, 1.6% and 1%, respectively. Rainfall was seasonally variable, with high rates in spring and summer but low rates in autumn and winter, while ion concentrations followed the reverse seasonal cycle. To evaluate deposition rates (DR) of different elements, average DR of each ion was calculated from a simple model. Most of the highest DRs of these substances occurred in Suzhou and Wuxi, located east and north of Lake Taihu, which shows there was considerable variation over the 5 stations. This regional pattern reflects local emissions from industry and agriculture, and suggests that steps need to be taken by local governments for particle emission reductions. The estimated annual inputs of TN and TP over the lake are 4722 and 75 t, respectively, which accounts for around 16.5% and 7.3% of the annual total external inputs of these nutrients. Primary productivity in Lake Taihu associated solely with wet deposition of nitrogen to the lake was estimated to be 7.03×10 6 mol C day −1. These results suggest that wet deposition can have significant impacts on the trophic status of Lake Taihu and that attention to nutrients in precipitation should be included in the management of external nutrient loads to the lake.

Hindcasting of nutrient loadings from its catchment on a highly valuable coastal lagoon: the example of the Fleet, Dorset, UK, 1866–2004

BackgroundNutrient loadings from its catchment upon The Fleet, a highly valuable coastal lagoon in Southern England, were hindcast for the period AD 1866–2004, using a catchment model, export coefficients, and historical data on land use changes, livestock numbers, and human population. Agriculture was the main nutrient source throughout, other inputs representing minor contributions. Permanent pasture was historically the main land use, with temporary grassland and cereals increasing during the mid-20th century. Sheep, the main 19th century livestock, were replaced by cattle during the 1930s.ResultsTotal nitrogen loadings rose from ca 41 t yr-1 during the late 19th century to 49–54 t yr-1 for the mid-20th, increasing to 98 t yr-1 by 1986. Current values are ca 77 t yr-1. Total phosphorus loads increased from ca 0.75 t yr-1 for the late 19th century to ca 1.6 t yr-1 for the mid-20th, reached ca 2.2 t yr-1 in 1986, and are now ca 1.5 t yr-1. Loadings rose most rapidly between 1946 and 1988, owing to increased use of inorganic fertilisers, and rising sheep and cattle numbers. Livestock were the main nutrient source throughout, but inputs from inorganic fertilisers increased after 1946, peaking in 1986. Sewage treatment works and other sources contribute little nitrogen, but ca 35% of total phosphorus. Abbotsbury Swannery, an ancient Mute Swan community, provides ca 0.5% of total nitrogen, and ca 5% of total phosphorus inputs.ConclusionThe Fleet has been grossly overloaded with nitrogen since 1866, climaxing during the 1980s. Total phosphorus inputs lay below 'permissible' limits until the 1980s, exceeding them in inner, less tidal parts of the lagoon, during the 1940s. Loadings on Abbotsbury Bay exceeded 'permissible' limits by the 1860s, becoming 'dangerous' during the mid-20th century. Phosphorus stripping at point sources will not significantly reduce loadings to all parts of the lagoon. Installation of 5 m buffer strips throughout the catchment and shoreline will marginally affect nitrogen loadings, but will reduce phosphorus inputs to the West Fleet below 'permissible' limits. Only a combination of measures will significantly affect Abbotsbury Bay, where, without effluent diversion, loadings will remain beyond 'permissible'.

Nitrogen, phosphorus, and energy waste outputs of four marine cage-cultured fish fed with trash fish

Trash fish used as aquafeeds in marine cage cultivation sometimes induced environmental risk. In this study, nitrogen, phosphorus, and energy waste outputs were measured in four marine cage-cultured carnivorous fish species – Sciaenops ocellatus, Plectorhynchus cinctus, Epinephelus coioides, and Rhabdosargus sarba – fed with trash fish for 6 weeks in laboratory. Waste outputs of cultured fish were divided into soft tissues in uneaten feed, bones in uneaten feed, scales in uneaten feed, soluble uneaten feed, solid faeces, soluble faeces, urine, caducous scales, and other parts. The results showed that an increase in 1 g of fish mass produced: 1) 34.4–67.2 mg nitrogen in urine, uneaten feed, faeces, and caduceus scales; 2) 3.4–10.9 mg phosphorus in uneaten feed, faeces, and caduceus scales; and 3) 12.0–23.8 kJ in metabolism, uneaten feed, urine, and caduceus scales. In the nutrient budget, urine was the most important component of nitrogenous waste and accounted for 7.8–14.4% of total nitrogen input. Bones and scales in uneaten feed carried the bulk of phosphorus waste, and these accounted for 4.1–13.8% of total phosphorus input. Metabolism was the largest energy consumed and it accounted for 12.0–20.8% of total energy input. The ratio of energy:nitrogen:phosphorus in waste outputs was 1.0–1.4:3.9–4.5:1. The information on nutrient and energy in waste output of the four fish in this study would help to assess and predict pollution of trash fish used as aquafeeds.

Fifty years of primary production measurements in the Baltic entrance region, trends and variability in relation to land-based input of nutrients

Inter-annual variations and long-term trends in phytoplankton primary production (PP) within the Baltic entrance region (the Kattegat and the Belt Sea) are presented and discussed. The study employs the core of Danish monitoring data, with measurements at 6–8 different sites from the past 20–50 years. Temporal development of the annual PP is compared with changes and variations in the land-based nutrient inputs and to other, independent, Swedish and Danish PP data. Spatial and seasonal variations based on annual and monthly PP, respectively, are evaluated. There are large variations on all scales; annual PP ranges from 50 to 500 g C m − 2, with maximum values in some Danish fjords and minimum values in open waters during the 1950s. The Kattegat and the Sound have a lower mean production (135–165 g C m − 2; 1981–2000) than the Great and Little Belts (185–220 g C m − 2). Compared to 1950s and 1960s, the daily PP has changed from being almost constant between March and October, to having two more distinct maxima, one in March and one between July and September. It is obvious that annual mean production has increased considerably since the 1950s, but also that this increase took place before 1980. For data after 1980, we find a co-variation between annual nutrient loads and regional mean PP; years of low total nitrogen (TN) and total phosphorus (TP) input to the region coincide with low PP and vice versa. Waste-water treatment and measures in agriculture have reduced the land-based input of TN by about 1/3 and input of TP by about 2/3 since the 1980s, enough to cause a substantial decrease in the surface water nutrient concentrations. A simultaneous, but weak downward trend in the regional mean PP can be seen up to 1997, after which the trend is broken. Higher production from 1998 is most likely an effect of changes in the method used for determination of PP.

Nutrient mass balances in semi-intensive shrimp ponds from Sonora, Mexico using two feeding strategies: Trays and mechanical dispersal

An experiment was conducted to determine the effect of two feeding practices — use of feeding trays (FT) and a mechanical feed dispersal device (FD) — on the growth performance and nutrient mass balances of white shrimp Litopenaeus vannamei. Cultured shrimp fed by feeding trays showed greater mean weight (32.3 ± 0.9 g) and yield than those fed by mechanical dispersal (29.5 ± 0.5 g). Feed added, shrimp survival and feed conversion were not significantly different between the two feeding strategies. Of the total input of nitrogen and phosphorus to the ponds fed by dispersion, 27.2% and 13.6% were recovered, respectively, yielding 2920 ± 30 kg/ha of shrimp. Ponds in which trays were used showed nitrogen and phosphorus recovery of 28.3% and 14.3%, respectively, and a yield of 3325 ± 153 kg/ha. The estimated environmental losses of nitrogen and phosphorus per ton of shrimp produced were 73.3 and 13.2 kg/ton, respectively, for the FD treatment; whereas in FT ponds losses were 70.6 and 12.8 kg/ton, respectively. This study showed the potential of feeding trays as a better strategy for shrimp culture that permits the addition of most feed rates by an improvement in yield of L. vannamei and a reduction of environmental losses of nitrogen and phosphorus in comparison to mechanical feed dispersion.

Impact of aquaculture on eutrophication in Changshou Reservoir

As a result of intensifying human activities around the Changshou Reservoir, water environmental quality has declined over the years. Water quality had been monitored from 1999 to 2002. The result indicated that the concentrations of total nitrogen (TN) and total phosphorus (TP) are high. The concentrations of phosphorus range from 0.037 mg/L to 0.444 mg/L, exceeding the critical value (0.02 mg/L) for eutrophication. The concentrations of total nitrogen and chlorophylla range from 0.70 mg/L to 4.18 mg/L and from 1.10 mg/m3 to 61.2 mg/m3, respectively. The eutrophication status of the water body was assessed using the method of integrated nutrition state index, which revealed that all sampling sites were eutrophicated from the year of 2001. About 69.6% of the annual total nitrogen input and 26% of the annual total phosphorus input originated from the upstreams. The contributions of nitrogen and phosphorus from precipitation to the water body are very small (0.9% and 0.3%, respectively) owing to their low contents (1.21 mg/L and 0.029 mg/L, respectively). Runoff is the secondarily important input source, which accounts for 19.0% of the total N input and 47.0% of the total P input, respectively. Attention should be paid to the aquaculture inputs, whose contributions account for 10.5% of the total N and 26.6% of the total phosphorus to the water body, respectively. Nutrient loads are estimated to be 118 gNm−2·a−1 and 8 gPm−2·a−1. About 69.4% of nitrogen and 79.7% of phosphorus input into the reservoir were retained in 2002.

Evidence for a delayed response of riverine phosphorus exports from increasing agricultural catchment pressures in the Lough Neagh catchment

Total phosphorus (TP) exports from the rivers draining into Lough Neagh increased between 1974 and 2000 despite lower TP inputs to the rivers from point sources. Over this period annual diffuse exports of dissolved reactive P (DRP) increased by 238%, from 17 to 57 kg P km−2 with an annual rate increase of 1.6 ± 0.3 kg P km−2 yr−1. Dissolved unreactive P exports increased by 0.4 ± 0.2 kg P km−2 yr−1, but particulate P exports did not increase. Annual exports of these three P fractions were positively correlated with annual runoff. The catchment of Lough Neagh has experienced an intensification of agriculture, with phosphorus inputs of manures and fertilizers to agricultural land increasing from 1,176 kg P km−2 yr−1 in 1925 to 3,823 kg P km−2 yr−1 in 2000. However 85% of this increase predated 1975. Increasing DRP exports after 1974 were better correlated with increasing soil P, and 70% of the increase in P accumulation by soils since 1925 occurred after 1974. Land use remained stable after 1974 with a historically low component of arable (>5%) and a dominance of grassland (<63%). The principal decade of intensification was in the 1940s, but this coincided with a greater arable component of land use. This period predated the increase in diffuse DRP exports. Intensively managed grasslands appear to be vulnerable to high DRP exports, reflecting surface application of manures, accumulation of soil P at the surface, and the creation of bypass flow pathways that facilitate the loss of P from soil to water.

Atmospheric Phosphorus Deposition in Ashiu, Central Japan – Source Apportionment for the Estimation of True Input to a Terrestrial Ecosystem

Atmospheric bulk depositions of soluble reactive phosphorus (SRP), soluble unreactive phosphorus (SUP), particulate inorganic phosphorus (PIP), particulate organic phosphorus (POP), total phosphorus (TP) and some other dissolved and particulate components were monitored for 3 years in Ashiu, Central Japan. The mean bulk depositions of SRP, SUP, PIP, POP, TP, dissolved components (Na, Mg, nss-Ca, K, V, Mo, nss-SO4) and particulate components (Al, Fe, Ti, Ca, Mg, Mn, Ba, Sr, Zn) were 175, 76, 136, 397, 783, 156,000, 10,900, 7450, 5470, 10.3, 1.52, 40,100, 13,200, 3590, 2630, 576, 624, 42.3, 30.2, 17.4, 8.2 μmol m−2 year−1, respectively. The value for TP deposition was in the lower range of previous literature. The low P deposition probably reflected the method applied to reduce the contribution of local particles, including (1) placement of samplers off the ground surface, (2) installation of multiple samplers, and (3) rejection of contaminated samples. Al data suggested that 15 ± 5% of TP was brought by lithogenic dust from East Eurasia. Nss-SO4 and Mo data and air-mass backward trajectories suggested that 39 ± 4% of TP was derived from coal combustion in China. It was speculated that the rest (47 ± 6%) of the TP deposition might be predominantly attributed to the contribution of local biogenic particles. Net atmospheric TP input (lithogenic dust and fossil fuel combustion) was almost equal to the TP outflow from Japanese forests on granitic soils.

Atmospheric and riverine inputs of metals, nutrients and persistent organic pollutants into the lagoon of Venice

Atmospheric deposition in the lagoon of Venice and river inputs from the watershed were collected and analysed from 1998 to 1999 using the same analytical methods. The input from riverine sources largely prevails (>70%) over that from the atmosphere for As, Cr, Fe, Mn, Ni, nitrogen and phosphorus. Equivalent amounts of Hg, Pb, PCBs, HCB are discharged into the lagoon from the two sources, whilst atmospheric inputs prevail for Cd, ammonia and dioxins. A comparison with figures of maximum allowable discharges (MAD) for various compounds, recently set by the Italian Ministry for the Environment, showed that total inputs (riverine + atmospheric) of trace metals were below the MAD thresholds only for Cr, Cu, Ni and Zn. The total inputs of Cu and Ni, and Cr and Zn were approximately 20 and 40% of the MAD limit, respectively. The total phosphorus input of 284 t was close to the imposed limit, whilst the inorganic nitrogen load alone (>4000 t) was much higher than the MAD for total nitrogen. For those metals (As, Cd, Hg and Pb) and persistent organic pollutants, such as polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) where the MAD states that the load should tend to ‘0’ (no discharge), the measured inputs of 4.8 (As) and 5.1 t (Pb), 151 (Cd) and 39 kg (Hg), 18 g (PCDD/Fs) and 440 mg (Toxicity Equivalents, TEQs, of PCDD/Fs) are by definition ‘above’ the MAD. The principal component analysis (PCA) of loading data and input profiles (markers) of production typologies showed that river and atmosphere contributions can be easily separated and recognised due to their different fingerprints. Riverine inputs were similar to chemical and glass work production markers, whereas atmospheric loadings were mainly influenced by chemical industry (PVC and VCM production), metallurgy and paper-mill.

The atmospheric deposition of phosphorus in Lake Victoria (East Africa)

Wet and dry atmospheric fluxes of total phosphorus (TP) and soluble reactive phosphorus (SRP) measured at four sites over a 12-month period were used to estimate lake-wide atmospheric phosphorus (P) deposition to Lake Victoria, East Africa. Atmospheric samples were collected in plastic buckets with top diameter of 25.5 cm by 30 cm deep. The highest P loading rates of 2.7 (TP) and 0.8 (SRP) kg ha−2 year−1 were measured at Mwanza compared to less than 1.9 (TP) and 0.65 (SRP) kg ha−2 year−1 measured in other three sites. By applying these loading rates to the lake surface, it was estimated that 13.5 ktons (13.5 × 103 kg) of TP were deposited annually into the lake from the atmosphere. Thirty-two percent of the total was found to be in the SRP form. Dryfall, a component ignored in previous studies exceeded wet deposition by contributing 75% of the total P input. However, materials deposited by dryfall made a lesser contribution to soluble form of phosphorus, as SRP concentrations in the wet samples were 2–3 times higher than SRP concentrations in dry samples. The annual fluxes of phosphorus measured on the south and western shores of Lake Victoria (1.8–2.7 kg ha−2 year−1) are near the upper range of similar fluxes measured in the tropics. In comparison with the existing estimates of municipal and runoff P inputs from other studies, it is estimated that atmospheric deposition represent 55% of the total phosphorus input to the Lake Victoria. The four sampling sites were fairly clustered and wet and dry P deposition data were collected from shore/land stations and applied to open lake areas to estimate lake-wide P deposition. In this regard, the estimates determined here should be viewed as a first order approximation of actual P load deposited into the lake.

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.

Incorporating phosphorus management considerations into wastewater management practice

Abstract Aspects of phosphorus management and its connection with wastewater management at a city level are explored here with the method of substance flow analysis (SFA) used to develop a phosphorus balance in Sydney, Australia, for the year 2000. The SFA results reveal that around 80% of the total phosphorus inputs into the system boundary are contained in food and detergent products. Only 50% of the total phosphorus imports leave the area, and around 90% of that amount is exported via treated wastewater discharge to the ocean. Wastewater treatment including water recycling is identified as a major activity influencing the movement of phosphorus; as such, attempts are made to link the phosphorus management options to the practice of wastewater management. The SFA method is used to evaluate different policy scenarios for the improvement of phosphorus management through static modeling with particular attention given to alternative decentralised options such as urine separation, composting toilet, and greywater recycling. Depending on the particular issue(s) of concern, different combinations of policy options are found to be most effective for the Sydney region based on the year 2000 data. Particularly effective options include, for example, phosphorus separation at source enabling beneficial reuse for agricultural purposes and changing consumers’ behaviour to minimise the use of phosphorus (hence limiting the need to mine phosphate rock).

Nutrient cycling in a strongly acidified mesotrophic lake

In contrast to the well‐known nutrient transformations in circumneutral lakes, acidified water bodies may exhibit significant changes in nutrient cycling due to changes in their chemistry and biology. In‐lake cycles of carbon (C), nitrogen (N), and phosphorus (P) were evaluated in the strongly acidified Plesné Lake (Central Europe). The lake tributaries had high concentrations of dissolved organic C (DOC), inorganic N, and total phosphorus (TP), resulting in annual averages of 644, 52, and 0.72 µmol L−1, respectively. Because of the absence of fish and largely reduced zooplankton, Plešne’ Lake has a “simplified” food web. The mass balance of nutrients was based on the major external inputs (tributaries and atmospheric deposition), internal sources and transformations (primary and bacterial production, biological decomposition of sedimenting seston and sediments), sedimentation, and outputs. External inputs of total organic C (TOC), total N (TN), and TP into Plesné Lake were 7,244, 864, and 8.6 mmol m−2 yr−1, respectively. Net primary production of particulate C (Cpart) and extracellularly released DOC were 3,205 and 613 mmol m−2 yr−1, respectively. Bacterial Cpart and total inorganic C production were both 1,518 mmol m−2 yr−1. Of the total internal and external inputs of TOC, TN, and TP, the in‐lake processes removed 4,551 (50% respiration, 40% sedimentation, and 10% photooxidation), 211 (74% sedimentation and 26% denitrification), and 4.6 (100% sedimentation) mmol m−2 yr−1, respectively. Compared to circumneutral lakes, nutrient cycling differed as follows: (1) Liberated orthophosphate from sedimenting seston was converted from a liquid to a particulate phase by colloidal aluminum (Al) in the hypolimnion and deposited. Similar abiotic P immobilization with Al removed 1.6 mmol m−2 yr−1 from the whole‐water column, thus reducing by ~20% the pool of potentially bioavailable P and contributing to a severe P limitation of biomass. (2) The cessation of nitrification due to long‐term water acidification led to an atypical situation in which the lake became a net source of NH4+ (30 mmol m−2 yr−1) because dissimilative liberation of NH4+ exceeded its assimilation.

Nitrogen and Phosphorus Cycling in Shrimp Ponds and the Measures for Sustainable Management

Six ponds of age 3 were selected 45 km north from Suzhou in the Tailake region, and research conducted on nitrogen and phosphorus cycling in P. vannanmei (Penaeus vannanme) ponds and M. nipponense (Macrobrachium nipponense) hatchery ponds under normal management. Two treatments each had three replications. The results confirmed that feed was the major path of nitrogen and phosphorus input, each accounted for 61.24% (193.81 kg ha(-1)) and 81.08% (45.20 kg ha(-1)) of the total nitrogen and phosphorus input for P. vannanme ponds; the values for M. nipponense ponds were 43.93% (86.31 kg ha(-1)) and 57.67% (14.61 kg ha(-1)), respectively. Water pumped into ponds contributed on average 83.57 kg ha(-1) nitrogen and 8.48 kg ha(-1) phosphorus for P. vannanmei ponds, and 87.48 kg ha(-1) nitrogen and 7.00 kg ha(-1) phosphorus for M. nipponense hatchery ponds. Shrimp harvest recovered 102.81 kg ha(-1) nitrogen (32.94% of the total nitrogen input) and 7.94 kg ha(-1) phosphorus (14.23% of the total phosphorus input) for P. vannanme ponds; and 43.94 kg ha(-1) nitrogen and 4.46 kg ha(-1) phosphorus for M. nipponense hatchery ponds. The sum of nitrogen losses through volatilization, denitrification and sedimentation was 173.62 and 122.39 kg ha(-1), 54.86% and 62.29% of the total nitrogen input for P. vannanme ponds and M. nipponense hatchery ponds, respectively. Sediment accumulated 41.46 and 14.63 kg ha(-1) phosphorus, 74.37% and 64.85% of the total phosphorus input for P. vannanm ponds and M. nipponense hatchery ponds. Draining and seeping caused 40.06 kg ha(-1) nitrogen (12.66% of total nitrogen input) and 6.36 kg ha(-1) phosphorus (11.40% of total phosphorus input) loss to the surrounding water from P. vannanme ponds in 114 days; 30.14 kg ha(-1) nitrogen (15.34% of the total input) and 4.45 kg ha(-1) phosphorus (17.57% of the total input) to channel water from M. nipponense hatchery ponds in 87 days, respectively. Countermeasures for sustainable pond management include improving feeds and feeding, sediment treatments, machine aerating, chemicals with no pollution, and integrated fish-shrimp cultivation. Management of water resources for pond and methods to reduce nitrogen and phosphorus loading into surrounding water from drainage are elucidated.

Reconstruction of the total N and P inputs from the IJsselmeer into the western Wadden Sea between 1935–1998

In this paper we reconstruct the Total Nitrogen (TN) and Total Phosphorus (TP) inputs into the western Wadden Sea from its major freshwater source the lake IJsselmeer between 1935–1998. The reconstruction is based on the TN and TP loads of the river Rhine at the German/Dutch border and follows the aquatic continuum approach to calculate loads further downstream in (1) the river IJssel feeding the IJsselmeer, and (2) the discharge of this lake into the western Wadden Sea. Our objectives are to determine (1) how the signal of changing nutrient loads of the Rhine is transferred downstream, and (2) how hydrological changes in the rivers-and-lake system affected the TN and TP discharges into the western Wadden Sea. Observational data from which TN and TP loads of the river Rhine could be calculated date back to the 1960s and we used background loads for European rivers for the period before World War II. The period in between was interpolated using the historic scenarios of watershed land use and management tested for the hypothetical Phison river (Billen and Garnier, 1997, Aquat. Microb. Ecol. 13, 3–17), adapted for the hydrology of the Rhine. The interpolations were constrained by loads of dissolved inorganic N and P compounds, for which data go back to the 1930s. Using the reconstructed loads of the river Rhine, TN and TP loads of the river IJssel and the lake IJsselmeer were calculated with simple mass balance models that were calibrated against data available from 1972–1993 onwards. Results show a gradual 12-fold increase of the TN discharge of the IJsselmeer into the Wadden Sea from 1935 to 1988, after which it decreased to levels still ∼5 fold those in 1935. The discharge of TP increased more abruptly in the early 1960s to values in 1983 ∼10 fold those before 1965, followed by a sharp decrease to values still ∼2.5 fold those before 1965. These patterns resemble those in the river Rhine, but are modified due to (1) variability of other sources to the lake, and (2) reduction of the retention capacity of the lake due to enormous land reclamation. TN:TP atomic ratios in the freshwater input to the Wadden Sea as high as 100 in 1995 were caused by successful P reduction programmes, less successful N reduction and N-rich inputs from smaller rivers and land runoff into the lake IJsselmeer. Land reclamation caused the lake's retention of TN to decrease step-wise from ∼70% to ∼45–50% and that of TP from 85% to 55–60% between 1950 and 1980.

Carbon and Nutrient Cycling at the Sediment-water Boundary in Western Lake Superior

Organic carbon and nutrient settling rates, benthic recycling rates, and material burial rates were measured in the western arm of Lake Superior. Organic carbon settling rates, measured using particle-intercepting sediment traps, averaged 2.3 mmol m −2 day −1 over the course of the experiment. Measured particle settling fluxes exhibit a minimum during winter and a maximum during spring. Sediment oxygen uptake rates measured throughout the basin average 2.2 ± 0.8 mmol m −2 day −1 (n = 16) and nitrate, soluble reactive phosphorus, and silicic acid efflux rates average 0.15 ± 0.07 (n = 25), 0.005 ± 0.006 (n = 23), and 1.34 ± 0.4 mmol m −2 day −1 (n = 26), respectively. Sediment solid-phase, particle settling rate, and benthic efflux data demonstrate that organic carbon, nitrogen, and biogenic silica are recycled at the sediment- water interface with an efficiency of ∼60% or greater in western Lake Superior. In contrast to these constituents, phosphorus recycling efficiency is lowest at sites close to the two major river inputs of (∼10%) and highest at our deepest site (∼40%). Despite these low recycling efficiencies for phosphorus, the benthic flux of phosphorous is an essential and dominant component to the lake's annual internal budget contributing ∼50% of the total annual phosphorus inputs to the water column.

A simulation of the Gulf of Finland ecosystem with a 3D model

Abstract. Comparison of simulations with a 3D eutrophication model with observation data for the Gulf of Finland showed that the model reproduced satisfactorily typical features of seasonal variability in the Gulf of Finland system, especially in the surface layers. However, as the model is driven by real atmospheric forcing for 1995–2000 and by climatically average river runoff and nutrient loads, it was unable to simulate the exact succession of events occurring in the deep layers of the gulf during this period. More time-specific data are needed both for prescription of boundary conditions and as validation criteria in order to further calibrate the model and test its performance. Key words: eutrophication, 3D modelling, hydrodynamics, biogeochemical cycles, validation, Baltic Sea, Gulf of Finland. INTRODUCTION The Gulf of Finland collects from its watershed about 20% of the terrestrial inputs of total nitrogen and phosphorus into the entire Baltic Sea (HELCOM, 1998). The eastern part of the gulf, which receives over 70% and 80% of the total phosphorus and nitrogen land loads to the gulf, respectively (Pitkanen et al., 2001), is even more subject to anthropogenic impact. The elevated trophic status of the gulf results in occasional cyanobacteria blooms, oxygen deficiency, macrofauna

Nutrient retention and nutrient-use efficiency in Phragmites australis stands after wasterwater application

The capacity of Phragmites australis to extract nutrients from its environment and to store them in plant tissue was studied in an infiltration wetland used for wastewater treatment. The aims of the study were to estimate the contribution of plant uptake to the overall nutrient removal efficiency of the wastewater treatment system and to determine measures to enhance the nutrient removal efficiency. The functional response of Phragmites australis to nutrient addition was studied at two levels of nutrient availability by comparing a wetland used for wastewater treatment with a natural, undisturbed wetland. In the nutrient-rich wastewater wetland, biomass production, nutrient content of plant tissue, shoot/root ratios, and translocation rates were much greater than in the natural wetland. In contrast, plant nutrient-use efficiencies of both nitrogen and phosphorus were much lower in the wastewater wetland. The lower nutrient-use efficiencies were probably due to (1) lower nutrient productivity, which was probably due to self-shading resulting in a lower photosynthetic activity, and (2) lower mean nutrient residence time, which can be explained by a higher litter production (higher shoot and leaf turnover). In the wastewater wetland, harvesting during winter removed only 9% of the total nitrogen input and 6% of the total phosphorus input associated with the loading of wastewater. The low nutrient removal efficiency by aboveground plant harvesting is caused by translocation of nutrients from shoots and leaves to rhizomes and roots in autumn. Nutrient removal efficiency of the wastewater wetland could be enhanced by 40–50% by harvesting at peak nutrient storage levels in the aboveground plant parts in August or September.

Phosphorus and dissolved silicon dynamics in the River Swale catchment, UK: a mass‐balance approach

AbstractThe internal riverine processes acting upon phosphorus and dissolved silicon were investigated along a 55 km stretch of the River Swale during four monitoring campaigns. Samples of river water were taken at 3 h intervals at sites on the main river and the three major tributaries. Samples were analysed for soluble reactive phosphorus, total dissolved phosphorus, total phosphorus, dissolved silicon and suspended solid concentration. Mass‐balances for each determinand were calculated by comparing the total load entering the river with the total load measured at the downstream site. The difference, i.e. the residual load, showed that there was a large retention of phosphorus and silicon within the system during the March 1998 flood event, but the other three campaigns produced net‐exports.Cumulative residual loads were calculated for each determinand at 6 h intervals throughout each campaign. This incremental approach showed that the mass‐balance residuals followed relatively consistent patterns under various river discharges. During stable low‐flow, there was a retention of particulate phosphorus within the system and also a retention of total dissolved phosphorus and soluble reactive phosphorus, most likely caused by the sorption of soluble phosphorus by bed‐sediments. In times of high river‐discharge, there was a mobilization and export of stored bed‐sediment phosphorus. During overbank flooding, there was a large retention (58% of total input) of particulate phosphorus within the system, due to the mass deposition of phosphorus‐rich sediment onto the floodplain. Soluble phosphorus was also retained within the system by sequestration from the water column by the high concentration of suspended solids.The dissolved silicon mass‐balance residuals had a less consistent pattern in relation to river discharge. There was a large retention of dissolved silicon during overbank flooding, possibly due to sorption onto floodplain soil, and net‐exports during periods of both stable low‐flow and rising limbs of hydrographs, due to release of dissolved silicon from pore‐waters. Copyright © 2001 John Wiley & Sons, Ltd.