Norbert A. Jaworski

Regional nitrogen budgets and riverine N & P fluxes for the drainages to the North Atlantic Ocean: Natural and human influences

We present estimates of total nitrogen and total phosphorus fluxes in rivers to the North Atlantic Ocean from 14 regions in North America, South America, Europe, and Africa which collectively comprise the drainage basins to the North Atlantic. The Amazon basin dominates the overall phosphorus flux and has the highest phosphorus flux per area. The total nitrogen flux from the Amazon is also large, contributing 3.3 Tg yr-1 out of a total for the entire North Atlantic region of 13.1 Tg yr-1. On a per area basis, however, the largest nitrogen fluxes are found in the highly disturbed watersheds around the North Sea, in northwestern Europe, and in the northeastern U.S., all of which have riverine nitrogen fluxes greater than 1,000 kg N km-2 yr-1.

Rising stream and river temperatures in the United States

Water temperatures are increasing in many streams and rivers throughout the US. We analyzed historical records from 40 sites and found that 20 major streams and rivers have shown statistically significant, long-term warming. Annual mean water temperatures increased by 0.009–0.077°C yr−1, and rates of warming were most rapid in, but not confined to, urbanizing areas. Long-term increases in stream water temperatures were typically correlated with increases in air temperatures. If stream temperatures were to continue to increase at current rates, due to global warming and urbanization, this could have important effects on eutrophication, ecosystem processes such as biological productivity and stream metabolism, contaminant toxicity, and loss of aquatic biodiversity.

Sources of nitrate in rivers draining sixteen watersheds in the northeastern U.S.: Isotopic constraints

The feasibility of using nitrogen and oxygenisotope ratios of nitrate (NO3−) forelucidating sources and transformations ofriverine nitrate was evaluated in a comparativestudy of 16 watersheds in the northeastern U.S.A. Stream water was sampled repeatedly at theoutlets of the watersheds between January andDecember 1999 for determining concentrations,δ15N values, and δ18Ovalues of riverine nitrate.In conjunction with information about land useand nitrogen fluxes,δ15Nnitrate andδ18Onitrate values providedmainly information about sources of riverinenitrate. In predominantly forested watersheds,riverine nitrate had mean concentrations ofless than 0.4 mg NO3−-N L−1,δ15Nnitrate values of lessthan +5‰, and δ18Onitratevalues between +12 and +19‰. This indicatesthat riverine nitrate was almost exclusivelyderived from soil nitrification processes withpotentially minor nitrate contributions fromatmospheric deposition in some catchments. Inwatersheds with significant agricultural andurban land use, concentrations of riverinenitrate were as high as 2.6 mg NO3−-NL−1 with δ15Nnitratevalues between +5 and +8‰ andδ18Onitrate values generallybelow +15‰. Correlations between nitrateconcentrations, δ15Nnitratevalues, and N fluxes suggest that nitrate inwaste water constituted a major, and nitrate inmanure a minor additional source of riverinenitrate. Atmospheric nitrate deposition ornitrate-containing fertilizers were not asignificant source of riverine nitrate inwatersheds with significant agricultural andurban land use. Although complementary studiesindicate that in-stream denitrification wassignificant in all rivers, the isotopiccomposition of riverine nitrate sampled at theoutlet of the 16 watersheds did not provideevidence for denitrification in the form ofelevated δ15Nnitrate andδ18Onitrate values. Relativelylow isotopic enrichment factors for nitrogenand oxygen during in-stream denitrification andcontinuous admixture of nitrate from theabove-described sources are thought to beresponsible for this finding.

Where did all the nitrogen go? Fate of nitrogen inputs to large watersheds in the northeastern U.S.A.

To assess the fate of the large amounts of nitrogen (N) brought into the environment by human activities, we constructed N budgets for sixteen large watersheds (475 to 70,189 km2) in the northeastern U.S.A. These watersheds are mainly forested (48–87%), but vary widely with respect to land use and population density. We combined published data and empirical and process models to set up a complete N budget for these sixteen watersheds. Atmospheric deposition, fertilizer application, net feed and food inputs, biological fixation, river discharge, wood accumulation and export, changes in soil N, and denitrification losses in the landscape and in rivers were considered for the period 1988 to 1992. For the whole area, on average 3420 kg of N is imported annually per km2 of land. Atmospheric N deposition, N2 fixation by plants, and N imported in commercial products (fertilizers, food and feed) contributed to the input in roughly equal contributions. We quantified the fate of these inputs by independent estimates of storage and loss terms, except for denitrification from land, which was estimated from the difference between all inputs and all other storage and loss terms. Of the total storage and losses in the watersheds, about half of the N is lost in gaseous form (51%, largely by denitrification). Additional N is lost in riverine export (20%), in food exports (6%), and in wood exports (5%). Change in storage of N in the watersheds in soil organic matter (9%) and wood (9%) accounts for the remainder of the sinks. The presence of appreciable changes in total N storage on land, which we probably under-rather than overestimated, shows that the N budget is not in steady state, so that drainage and denitrification exports of N may well increase further in the future.

A watershed nitrogen and phosphorus balance : the upper Potomac river basin

Nitrogen and phosphorus mass balances were estimated for the portion of the Potomac River basin watershed located above Washington, D.C. The total nitrogen (N) balance included seven input tource terms, six sinks, and one “change-in-storage” term, but was simplified to five input terms and three output terms. The phosphorus (P) balance had four input and three output terms. The estimated balances are based on watershed data from seven information sources. Major sources of nitrogen are amimal waste and atmospheric deposition. The major sources of phosphorus are animal waste and fertilizer. The major sink, for nitrogen is combined denitrification, volatilization, and change-in-storage. The major sink for phosphorus is change-in-storage. River exports of N and P were 17% and 8%, respectively, of the total N and P inputs. Over 60% of the N and P were volatilized or stored. The major input and output terms on the budget are estimated from direct measurements, but the change-in-storage term is calculated by difference. The factors regulating retention and storage processes are discussed and research needs are identified.

Estuaries of the Northeastern United States: Habitat and Land Use Signatures

Geographic signatures are physical, chemical, biotic, and human-induced characteristics or processes that help define similar or unique features of estuaries along latitudinal or geographic gradients. Geomorphologically, estuaries of the northeastern U.S., from the Hudson River estuary and northward along the Gulf of Maine shoreline, are highly diverse because of a complex bedrock geology and glacial history. Back-barrier estuaries and lagoons occur within the northeast region, but the domiant type is the drowned-river valley, often with rocky shores. Tidal range and mean depth of northeast estuaries are generally greater when compared to estuaries of the more southern U.S. Atlantic coast and Gulf of Mexico. Because of small estuarine drainage basins, low riverine flows, a bedrock substrate, and dense forest cover, sediment loads in northeast estuaries are generally quite low and water clarity is high. Tidal marshes, seagrass meadows, intertidal mudflats, and rocky shores represent major habitat types that fringe northeast estuaries, supporting commercially-important fauna, forage nekton and benthos, and coastal bird communities, while also serving as links between deeper estuarine waters and habitats through detritus-based pathways. Regarding land use and water quality trends, portions of the northeast have a history of over a century of intense urbanization as reflected in increased total nitrogen and total phosphorus loadings to estuaries, with wastewater treatment facilities and atmospheric deposition being major sources. Agricultural inputs are relatively minor throughout the northeast, with relative importance increasing for coastal plain estuaries. Identifying geographic signatures provides an objective means for comparing the structure, function, and processes of estuaries along latitudinal gradients.

Sources of nutrients and the sacle of eutrophication problems in estuaries

A comprehensive analysis of external sources of nutrients is presented including an impact, comparison of external loadings, and the resulting scale of eutrophication. The major emphasis of the analysis is on nitrogen and phosphorus.

Forest nitrogen sinks in large eastern U.S. watersheds: estimates from forest inventory and an ecosystem model

The eastern U.S. receives elevated rates of Ndeposition compared to preindustrial times, yetrelatively little of this N is exported indrainage waters. Net uptake of N into forestbiomass and soils could account for asubstantial portion of the difference between Ndeposition and solution exports. We quantifiedforest N sinks in biomass accumulation andharvest export for 16 large river basins in theeastern U.S. with two separate approaches: (1)using growth data from the USDA ForestServices Forest Inventory and Analysis (FIA)program, and (2) using a model of forestnitrogen cycling (PnET-CN) linked to FIAinformation on forest age-class structure. Themodel was also used to quantify N sinks in soiland dead wood, and nitrate losses below therooting zone. Both methods agreed that netgrowth rates were highest in the relativelyyoung forests on the Schuylkill watershed, andlowest in the cool forests of northern Maine. Across the 16 watersheds, wood export removedan average of 2.7 kg N ha−1 yr−1(range: 1–5 kg N ha−1 yr−1), andstanding stocks increased by 4.0 kg N ha−1yr−1 (−3 to 8 kg N ha−1 yr−1). Together, these sinks for N in woody biomassamounted to a mean of 6.7 kg N ha−1yr−1 (2–9 kg N ha−1 yr−1), or73% (15–115%) of atmospheric N deposition. Modeled rates of net N sinks in dead wood andsoil were small; soils were only a significantnet sink for N during simulations ofreforestation of degraded agricultural sites. Predicted losses of nitrate depended on thecombined effects of N deposition, and bothshort- and long-term effects of disturbance. Linking the model with forest inventoryinformation on age-class structure provided auseful step toward incorporating realisticpatterns of forest disturbance status acrossthe landscape.

A Suggested Approach for Developing Estuarine Water Quality Criteria for Management of Eutrophication

A conceptual approach for developing water quality criteria for eutrophication management is suggested. The three basic components of the framework include source ambient relationships, effects, and impact analyses. The approach focuses on a conceptual method for developing decision-making criteria as opposed to the classical water quality criteria of a single value of limitation. The approach to developing water quality criteria for eutrophication management provides an analysis framework of response relationships which can be readily incorporated into water quality standard-setting processes that include environmental considerations and technological and economic factors.

A status report on the U.S. national dioxin study

Abstract In 1983, the US Environmental Protection Agency (EPA) embarked on an extensive investigation of the presence and extent of contamination of the national environment by CDDs/CDFs. This status report is a prelude to a final report to be delivered to the US Congress in December, 1985.