Wet Deposition Of Nitrate Research Articles

Nitrogen Isotopes as Indicators of NOx Source Contributions to Atmospheric Nitrate Deposition Across the Midwestern and Northeastern United States

Global inputs of NO(x) are dominated by fossil fuel combustion from both stationary and vehicular sources and far exceed natural NO(x) sources. However, elucidating NO(x) sources to any given location remains a difficult challenge, despite the need for this information to develop sound regulatory and mitigation strategies. We present results from a regional-scale study of nitrogen isotopes (delta15N) in wet nitrate deposition across 33 sites in the midwestern and northeastern U.S. We demonstrate that spatial variations in delta15N are strongly correlated with NO(x) emissions from surrounding stationary sources and additionally that delta15N is more strongly correlated with surrounding stationary source NO(x) emissions than pH, SO4(2-), or NO3- concentrations. Although emission inventories indicate that vehicle emissions are the dominant NO(x) source in the eastern U.S., our results suggest that wet NO3- deposition at sites in this study is strongly associated with NO(x) emissions from stationary sources. This suggests that large areas of the landscape potentially receive atmospheric NO(y) deposition inputs in excess of what one would infer from existing monitoring data alone. Moreover, we determined that spatial patterns in delta15N values are a robust indicator of stationary NO(x) contributions to wet NO3- deposition and hence a valuable complement to existing tools for assessing relationships between NO3- deposition, regional emission inventories, and for evaluating progress toward NO(x) reduction goals.

Seasonal variability of NOx emissions over east China constrained by satellite observations: Implications for combustion and microbial sources

Observations of tropospheric column densities of NO2 obtained from the Global Ozone Monitoring Experiment (GOME) for a 3‐year period (1997, 1998, and 2000) are used to derive average seasonal variations in surface emissions of NOx from east China (100–123°E, 20–42°N). The retrieval allows for zonal variations in the contribution of the stratosphere to the NO2 column and removes a bias of ±10% on the seasonality of retrieved columns introduced by cloud screening. The top‐down inventory is constructed using an inversion approach with a global 3‐D chemical transport model (GEOS‐Chem) and combined subsequently with the a priori inventory to develop an a posteriori inventory. The contribution of background NO2 arising from nonsurface sources (lightning) and long‐range transport of emissions originating outside of east China is accounted for in the inversion. The a posteriori estimate of overall emissions for east China, 4.66 Tg N/yr (±30% uncertainty), is 33% higher than the a priori value and is shown to improve agreement with surface measurements of nitrate wet deposition and concentrations of NOy observed in China. On the basis of multiple constraints on the spatial and seasonal variations of combustion and microbial processes, the a posteriori inventory is partitioned among emissions from biomass burning, fuel combustion, and microbial activity (or soil emissions). Emission of NOx from biomass burning in east China is estimated as 0.08 TgN/yr ± 50% in the a posteriori inventory, increased by about a factor of 2 from the a priori estimate. The resulting a posteriori inventory for fuel combustion (3.72 TgN/yr ± 32%) is about 15% higher than the a priori and exhibits a distinct maximum in winter, in contrast to the weak seasonality indicated in the a priori inventory. The a posteriori value for the microbial source of NOx (0.85 TgN/yr ± 40%) is about a factor of 3 higher than the a priori value, amounting to 23% of combustion sources for east China and significantly higher than a priori value of 7%. The microbial source is unimportant in winter. It peaks in summer, accounting for as much as 43% of the combustion source for that season, and is significant also in spring and fall. This seasonality is attributed to the timing of fertilizer application and to the influence of seasonally variable environmental factors including temperature and precipitation.

Temporal Trends of Non-sea Salt Sulfate and Nitrate in Wet Deposition in Japan

Temporal trends of non-sea salt (nss-) sulfate and nitrate were analyzed from nationwide precipitation chemistry measurements provided by the Ministry of the Environment (MOE) for the 1988–2002 fiscal years (April–March). The concentrations and deposition of nss-sulfate were found to be decreasing, and those of nitrate were stable or slightly increasing at most sites. These deposition trends were discussed from the viewpoint of emissions of SO2 and NOX during the period of interest. Because monitoring techniques have changed in the number of active sites, samplers, and analytical methods during the operation period, the median of all annual depositions measured in Japan in a specific year was selected as the annual representative. The contribution of specific emission sources was also calculated for 1990 on the basis of the nss-sulfate and nitrate deposition in Japan obtained with a model simulation in which the model did not include volcanic emissions from Mt. Oyama, Miyakejima Island, which began to erupt suddenly and violently in 2000. For nss-sulfate, the calculated deposition agrees well with the intensity and trends of the median up to 1999. After 2000, a higher deposition than calculated in the preceding years was evident, which is attributable to the volcanic SO2 from Mt. Oyama. For nitrate, both the calculated and observed depositions were slightly increasing; however, the calculation was found to exceed the observation.

Changes in precipitation chemistry in Lithuania for 1981–2004

This paper considers the spatial and temporal variability in concentrations of the potentially acidifying ions in precipitation in Lithuania during the 1981-2004 period. Chemical analysis of precipitation included measurements of pH, conductivity, sulfate (SO4(2-)), nitrate (NO3-), chloride (Cl-), ammonium (NH4+), sodium (Na+), potassium (K+), and calcium (Ca2+). Temporal trends in the potentially acidifying ion concentrations in precipitation and wet deposition were evaluated using the non-parametric Mann-Kendall test and Sen's slope estimator. A statistically significant decline was observed in non-sea salt sulfate (nssSO4(2-)) and hydrogen (H+) ions concentrations (82% and 79%, respectively) and wet depositions (88% and 74%, respectively). Temporal trends both in concentration and wet deposition of nitrate and ammonium were not as pronounced as trends in sulfate concentration. Analysis of air mass backward trajectories was applied to reveal the influence of air mass originating in different regions on wet deposition of acidifying species in Lithuania. Sector analysis clearly showed that wet deposition of sulfur and nitrogen in Lithuania is to a large extent anthropogenic and the main source regions of acidifying species contributing to wet deposition in Lithuania are in South and Central Europe.

Changes in the atmospheric deposition of acidifying compounds in the UK between 1986 and 2001

Emissions of a precursor of acidity in precipitation, sulphur dioxide (SO 2), declined in the UK and the EU (15) by 71% and 72%, respectively, between 1986 and 2001, while nitrous oxide emissions declined by about 40%. Acidity in UK precipitation and the deposition of sulphate in precipitation halved during this period, but reductions were larger in the English Midlands than at the west coast and in high rainfall areas (>2000 mm). There is evidence that the smaller reductions in sulphur deposition in the west and south are due in part to shipping sources of SO 2. Reductions in sulphur dry deposition (74%) are larger than in wet deposition (45%), due to changes in the canopy resistance to dry deposition. For reduced nitrogen, there has been a small (10%) reduction in emissions and deposition, while for oxidized nitrogen, a substantial reduction in emissions (40%) occurred but wet deposition of nitrate changed by less than 10%.

Modelling the deposition of atmospheric oxidised nitrogen and sulphur to the United Kingdom using a multi-layer long-range transport model

Abstract Deposition of sulphur and oxidised nitrogen have been estimated for the United Kingdom (UK) for 1996 using an atmospheric transport model (FRAME, Fine Resolution Atmospheric Multi-pollutant Exchange). Firstly, the modelled deposition is compared with measurement based estimates of NEGTAP (National Expert Group on Transboundary Air Pollution). Secondly, the modelled wet deposition and surface air concentrations are compared with measurements from the UK's monitoring networks using linear regression. FRAME gives 65 and 102 ktonnes(kt) for oxidised nitrogen dry and wet UK deposition, respectively, compared with the NEGTAP estimation of 87 and 91 kt . The modelled contributions of sulphur dry and wet deposition are 138 and 200 kt , respectively, compared with the NEGTAP estimation of 125 and 171 kt . FRAME is found to perform well for nitrogen dioxide concentrations and nitrate wet deposition, but the concentration and subsequent dry deposition of nitric acid is underestimated. Deposition of sulphur and sulphur dioxide surface concentrations are coherent with the NEGTAP estimation but they are slightly overestimated by FRAME. The paper also emphasises the uncertainties associated with the model when used to assess the effects of abatement policies.

Numerical Approach for the Effect of Size Distribution of Rain Drop on the Wet Deposition of Nitrate

Numerical Approach for the Effect of Size Distribution of Rain Drop on the Wet Deposition of Nitrate

Transfer of reactive nitrogen in Asia: development and evaluation of a source–receptor model

A simple model of chemistry and transport, ATMOS-N, has been developed to calculate source–receptor relationships for reactive nitrogen species within Asia. The model is intended to support discussion of energy and environmental issues in Asia, to compare sulfate and nitrate contributions to regional acidification, and to estimate how each nation's acid deposition and air quality relates to domestic versus foreign emissions. ATMOS-N is a Lagrangian “puff” model in which non-interacting puffs of emissions are advected horizontally and mixed between three vertical layers. Results are compared with wet nitrate deposition observations in Asia. On an annual average, the model estimates that long-range transport contributes a significant percentage of total nitrate deposition throughout east Asia. China, the largest emitter of the region, contributes 18% to nitrate deposition in Taiwan, 18% in Japan, 46% in North Korea, and 26% in South Korea. South Korea contributes 12% to nitrate deposition in Japan, due to its close upwind proximity. Compared with total acid deposition (nitrate+sulfate), nitrate contributes 30–50% over northern Japan, 30–60% in India, and 50–90% in southeast Asia where biomass burning emits high levels of NO x . The percentage contribution of nitrate is very low in China, where emissions and deposition of sulfur are extraordinarily high.

Trends in sulphate and nitrate wet deposition over the United Kingdom: 1986–1999

Since 1986 annual wet deposition of non-sea-salt sulphur has decreased over all regions of the United Kingdom, with the largest decrease in eastern areas. Nationally wet deposited sulphur has decreased by about one-third compared with an approximately two-thirds decrease in sulphur dioxide emissions. Over the same period daily measurements of sulphur dioxide and particulate sulphate concentrations at a small number of sites showed a statistically significant decrease at all but the most remote locations. The comparative magnitude of the changes in UK emissions and wet deposition suggests some change in the partitioning between wet and dry sulphur deposition. Trajectory analyses of precipitation events show that background sulphate deposition has not changed significantly in northwestern coastal regions, where it accounts for approximately half of the total. Wet nitrate deposition has decreased at a slower rate and increased slightly in some remote western areas. Sector analyses suggest that this increase is linked with increased deposition during easterly airflow while particulate sulphate concentrations in these airmasses have decreased. Nitrate now accounts for at least one-third of the acidifying effect of the combined wet deposition of non-sea-salt sulphate and nitrate over all parts of the United Kingdom.

Wet Deposition of Nitrate and Ammonium over the Japanese Archipelago

Wet Deposition of Nitrate and Ammonium over the Japanese Archipelago

Annual nitrogen budget of a temperate coastal barrier salt-marsh system along a productivity gradient at low and high marsh elevation

Abstract An annual nitrogen budget was established for a temperate back barrier salt-marsh system along a productivity gradient at low and high marsh elevation. We measured plant biomass and nitrogen content in three plant compartments to deduce plant N-allocation patterns. Measurements were done along a successional sequence in a salt-marsh system. In addition, N-mineralization, wet and dry atmospheric N-deposition and sediment N-deposition were measured. Plant-species dominance changed along the successional sequence. In early stages, Elymus farctus and Spergularia media formed a large part of total plant biomass. Festuca rubra and Puccinellia maritima were dominant at intermediate stages, whereas Elymus pycnanthus and Limonium vulgare were dominant at late stages of succession. Shoot biomass was highest in June, whereas litter biomass was highest in September and December. Root biomass formed by far the largest fraction of total plant biomass, especially at a low-marsh elevation. Wet deposition of nitrate and ammonium was 1.7 g N m −2 yr −1 , whereas throughfall deposition (dry and wet deposition) amounted to 2.1–3.6 g N m −2 yr −1 , and was positively related to the height of an artificial plant canopy. Sediment organic nitrogen deposition rate was 0.3–5.4 g N m −2 yr −1 , and negatively related to marsh elevation. Nitrogen mineralization rate increased from 2.5–2.8 g N m −2 yr −1 in young marshes towards 8.0–12.7 g N m −2 yr −1 at older marshes, depending on marsh elevation. At a low-marsh elevation, plant N-availability depended equally on tidal N, atmospheric N and mineralized N, especially in young marshes, whereas the decomposition pathway became more important in older marshes. Tidal N contributed most to ecoystem N-accumulation rate at early successional stages, whereas atmospheric N was more important at later stages. Tidal influence was low at high-marsh elevation sites. Here, atmospheric deposition was the dominant exogenous nitrogen source both in young and old marshes.

Comparison of emissions of nitrogen and sulfur oxides to deposition of nitrate and sulfate in the USA by state in 1990

Many naturally occurring and human-induced activities result in the emission of nitrogen- and sulfur-containing compounds into the atmosphere. Precipitation is an important process by which compounds are scavenged from the atmosphere and deposited onto the earth's surface. The purpose of this paper is to compare the emissions of nitrogen oxides (NO x) and sulfur dioxide (SO 2) in each of the 48 continguous states in the USA with measured wet deposition of nitrate (NO 3 −) and sulfate (SO 4 2−) in each state for the year 1990. With one exception (Vermont), wet deposition of N as nitrate was less than emissions of N as nitrogen oxides on a statewide basis in 1990. The median wet N deposition/emission value was 0.21. Wet plus dry N deposition of nitrate was estimated to represent 43% of NO x emissions in North Carolina. Wet deposition of S was less than emissions in 1990 in all but five states (Vermont, Maine, Arkansas, Nebraska, and South Dakota). The median value of wet deposition of sulfate/SO 2 emissions was 0.34. In North Carolina, dry deposition of sulfate was estimated to represent an additional 21% of emissions, so that total deposition accounted for 60% of S emissions. Net transport of N and S is likely an important part of the discrepancy between emissions and deposition.

Oxidized Nitrogen in the Remote Pacific: The Role of Electrical Discharges over the Oceans

Simulations of oxidized nitrogen performed withglobal transport tracer models systematicallyunderestimate the concentrations of total nitrate atremote marine locations in the Mid-Pacific. Higheremission rates in the models of nitrogen oxides(\({\text{NO}}_x = {\text{NO + NO}}_{\text{2}} \)) from continental sources or alarger influx from the stratosphere do not seem tobe able to account for the shortfall. We are led toconclude that there has to be a substantial sourcelocated in oceanic areas. We speculate that\({\text{NO}}_x \)-emission from electrical discharges overthe oceans could be the source we are looking for.Airborne observations of atmospheric concentrationsof oxidized nitrogen and ozone in the remoteatmosphere and observations of nitrate wetdeposition in remote sites are used as additionalconstraints to check the plausibility of thishypothesis. We find that a larger emission of\({\text{NO}}_x \) due to lightning activity over the oceansindeed results in a much improved simulation oftotal nitrate in the remote Pacific, particularly inthe Equatorial and Tropical South Pacific and thatsuch a scenario is generally consistent withavailable observations of nitrate wet deposition andatmospheric concentrations of oxidized nitrogen andozone. An alternative hypothesis is that there is ahitherto unknown in situ source of \({\text{NO}}_x \) over thePacific Ocean.

Atmospheric sulfur and nitrogen in West Java

Wet-only rainwater composition on a weekly basis was determined at four sites in West Java, Indonesia, from June 1991 to June 1992. Three sites were near the extreme western end of Java, surrounding a coal-fired power station at Suralaya. The fourth site was ∼100 km to the east in the Indonesian capital, Jakarta. Over the 12 months study period wet deposition of sulfate at the three western sites varied between 32–46 meq m−2 while nitrate varied between 10–14 meq m−2. Wet deposition at the Jakarta site was systematically higher, at 56 meq m−2 for sulfate and 20 meq m−2 for nitrate. Since sulfate and nitrate wet deposition fluxes in the nearby and relatively unpopulated regions of tropical Australia are both only ∼5 meq m−2 anthropogenic emissions of S and N apparently cause significant atmospheric acidification in Java. It is possible that total acid deposition fluxes (of S and N) in parts of Java are comparable with those responsible for environmental degradation in acid-sensitive parts of Europe and North America.

Numerical modeling of long-range transport of acidic species in association with mesoβ-convective-clouds across the Japan sea resulting in acid snow over coastal Japan—II. Results and discussion

Abstract The acid snow/rain model [describedin Part I, Kitada et al., Atmospheric Environment 27A , 1061–1076, 1993] was applied to investigate transport/transformation/deposition of acidic species in association with snow-precipitating cloud over the Japan Sea in winter. The model results showed: (1) The snow-precipitating clouds generated by relatively weak convective motions tend to trap aerosols of sulfate and nitrate and soluble gases such as SO 2 and HNO 3 below cloud levels, thus keeping their concentrations at higher levels than those for no-cloud situations. The mechanisms involved are: transfer of gas- and aerosol-phase species to cloud-phase through absorption and nucleation scavenging, then their transfer from cloud to snow through riming, and subsequent release from sublimating snow back to gas- and aerosol-phases below cloud base. (2) In-cloud oxidation enhanced the overall conversion of SO 2 to SO 4 2− by some 25% with respect to no-cloud situation after 12 h. Furthermore, contributions to the oxidation were 77.4%, 21.1% and 1.5% for S(IV)H 2 O 2 , S(IV)O 2 with catalysts of Fe 3+ + Mn 2+ and S(IV)O 3 reactions, respectively. (3) The sulfate wet deposited by precipitating snow for 12 h was due mostly to in-cloud scavenging and in-cloud oxidation, i.e. 66% by nucleation scavenging and the remaining by in-cloud oxidation of S(IV), while the contribution of below-cloud scavenging was negligible. (4) The adsorption process of HNO 3 onto the surface of falling snow was found to account for major below-cloud scavenging of snow, and thus in contrast to SO 4 2− , the below-cloud scavenging contributed very significantly to the nitrate wet deposition. Throughout the stimulation, below-cloud scavenging was responsible for 75% of the snow-NO 3 − formation. Therefore, taking account of this process in acid snow models is important.

Reaction of N2O5 on tropospheric aerosols: Impact on the global distributions of NOx, O3, and OH

Using a three‐dimensional global model of the troposphere, we show that the heterogeneous reactions of NO3 and N2O5 on aerosol particles have a substantial influence on the concentrations of NOx, O3, and OH. Due to these reactions, the modeled yearly average global NOx burden decreases by 50% (80% in winter and 20% in summer). The heterogeneous removal of NOx in the northern hemisphere (NH) is dominated by reactions on aerosols; in the tropics and southern hemisphere (SH), with substantial smaller aerosol concentrations, liquid water clouds can provide an additional sink for N2O5 and NO3. During spring in the NH subtropics and at mid‐latitudes, O3‐concentrations are lowered by 25%. In winter and spring in the subtropics of the NH calculated OH concentrations decreased by up to 30%. Global tropospheric average O3 and OH burden (the latter weighted with the amount of methane reacting with OH) can drop by about 9% each. By including reactions on aerosols, we are better able to simulate observed nitrate wet deposition patterns in North America and Europe. O3 concentrations in springtime smog situations are shown to be affected by heterogeneous reactions, indicating the great importance of chemical interactions resulting from NOx and SO2 emissions. However, a preliminary analysis shows that under present conditions a change in aerosol concentrations due to limited SO2 emission control strategies (e.g., reductions by a factor of 2 in industrial areas) will have only a relatively minor influence on O3 concentrations. Much larger reductions in SO2 emissions may cause larger increases in surface O3 concentrations, up to a maximum of 15%, if they are not accompanied by a reduction in NOx or hydrocarbon emission.

Wet deposition monitoring and modelling in New Brunswick — An area dominated by wet deposition due to long-range transport

Abstract Two wet deposition monitoring networks, the Coleson Cove Precipitation Monitoring Network (CCPMN) (12 stations) located in the Coleson Cove-Saint John area of south New Brunswick, and the Expanded New Brunswick Precipitation Monitoring Network (ENBPMN) (6 stations) covering the remainder of the province, were established in May 1988. The monitoring networks and a complementary modelling study were implemented to assess the relative contributions of local and distant sources to wet deposition in New Brunswick. Quality assurance/quality control activities for the networks included independent external audits, collocated samplers at one site and comparisons of weekly measurements at the ENBPMN sampler and the Canadian Air and Precipitation Monitoring Network (CAPMoN) sampler which makes daily measurements. The intercomparisons provided reassurance that the networks provided high quality data. Analysis of 2 years (June 1988–May 1990) data from the networks included routine statistical analyses for acid rain chemistry as well as analysis of 1 year of daily back trajectory data from Harcourt, New Brunswick. Three-day back trajectories determined at 12-h intervals from Harcourt on days with precipitatio showed that air masses originate mainly from regions in Quebec, Ontario and northeast U.S.A. which are known to have high sulphur oxide emissions. Some 18 trajectories were associated with 50% of the wet sulphate deposition and over 200 trajectories with 75% of the deposition in the 1-year period ending 31 May 1989. The MESOPUFF model, applied to an 800 km by 800 km domain that included the entire province of New Brunswick, was used to make predictions of wet sulphate and nitrate deposition at each of the wet deposition monitoring stations for a 2-year period, 1 June 1988-31 May 1990. Model predictions averaged over all receptors due to all sources in the model domain accounted for 7–25% of the measured seasonal average wet sulphate deposition and less than 3% of the measured wet nitrate deposition at all monitoring stations. Wet deposition in New Brunswick is thus dominated by distant sources through long-range transport. The model estimated that the oil-fired Coleson Cove thermal generating station contributed between 7% and 16% to the seasonal wet sulphur deposition and less than 3% of the seasonal wet nitrogen deposition at monitoring stations in the Coleson Cove-Saint John area. The estimates for wet nitrogen deposition are limited by the NO χ emissions information which is considered less reliable than SO 2 emissions information.

Trace gas concentrations and meteorology in rural Virginia: 2. Reactive nitrogen compounds

In this second of a two‐part paper on the air chemistry of the Big Meadows site in Shenandoah National Park, Virginia, we present measurements of reactive nitrogen compounds that play important roles in atmospheric photochemistry and acidity, and as nutrients in soil and water. These compounds are, however, poorly understood in terms of spatial and temporal variability. Measurements of nitric oxide, NO, and total reactive nitrogen, NOy, were made for over a year during 1988 and 1989 at a mountain site that we feel is representative of the regional tropospheric composition. We also measured total nitrate (HNO3 + NO3−) for three weeks during this period. For the whole year, the mean, standard deviation, (and median) NOy and daytime NO mixing ratios were 5.1±3.1 (4.3) ppbv and 0.59±0.94 (0.23) ppbv, respectively. A histogram for NOy appears to conform to a lognormal distribution, but fails a χ2 test of significance at the 0.05 level. The speciation of NOy indicates considerable photochemical aging, except in winter. Over the year during daylight, the median ratio NO/NOy was 0.06. Total nitrate (measured in August and September) accounted for 39% of the total NOy. Total reactive nitrogen shows no appreciable diurnal cycle, but NO, NOy, and the ratio NO/NOy show a summer minimum. For winter, spring, summer, and fall, the mean (and median) NOy mixing ratios were: 5.7±3.3 (5.0), 5.4±3.2 (4.4), 4.0±2.1 (3.5), and 5.2±3.2 (4.4) ppbv, respectively. Similarly, seasonally averaged daytime NO values were: 0.95±1.07 (0.61), 0.66±0.93 (0.28), 0.18±0.29 (0.13), and 0.70±1.10 (0.30) ppbv. Wet deposition of nitrate shows the opposite seasonality; we estimate the lifetime of NOy with respect to wet deposition to be 2.7 days in summer and 5.8 days in winter. Ozone and NOy were positively correlated in the summer and negatively correlated in the winter. Carbon monoxide and NOy were positively correlated in all seasons. The slope of a scatter plot of CO vs. NOy, 4.85, provides a lower limit to the molar emissions ratio of CO and NOx. Emissions inventories give a ratio of 4.15.

Atmospheric input of inorganic nitrogen species to the Kiel Bight

The atmospheric input of inorganic nitrogen species to the Kiel Bight (south-west Baltic Sea) is characterized. This characterization is based on marine precipitation samples collected at Kiel Lighthouse in weekly intervals during a whole year, using wet-only and bulk-sample methods. The temporal patterns of nitrate and ammonium concentrations are highly variable, with less variability during summer. Maximum concentrations were found in winter. The annual precipitation weighted mean concentrations are 124 μmol·dm−3 for nitrate and 172 μmol·dm−3 for ammonium. Nitrite concentrations were low, its contribution to wet deposition being thus negligible (on average only 0.3% of the wet deposition of nitrate plus ammonium). Dry deposition represents approximately one third of the total input of airborne nitrogen species. Wet and dry deposition represent an annual input of around 5000 tons of nitrogen to the Kiel Bight (2571 km2), being a significant contribution to its total nitrogen content (5900 tons in winter). The hypothesis of a triggering effect of intense nitrogen wet deposition pulses for summer phytoplankton blooms is raised and a possible relationship of phytoplankton patchiness with these deposition patterns to the sea is suggested.

On the relationship between precipitation amount and wet deposition of nitrate and ammonium

Precipitation collected as wetfall-only on a weekly basis at two sites in the Western Baltic was analyzed for nitrate and ammonium. Both concentration and wet deposition of nitrate and ammonium showed a highly significant correlation with precipitation amount. The relationship between concentration and precipitation amount is described by an inverse half-power law, while wet deposition of nitrate and ammonium is characterized by a dependence on the square root of precipitation amount. This relationship governing wet deposition is shown to be a consequence of the dependence of concentration on precipitation amount.