Douglas A. Burns

Who needs environmental monitoring

Environmental monitoring is often criticized as being unscientific, too expensive, and wasteful. While some monitoring studies do suffer from these problems, there are also many highly successful long-term monitoring programs that have provided important scientific advances and crucial information for environmental policy. Here, we discuss the characteristics of effective monitoring programs, and contend that monitoring should be considered a fundamental component of environmental science and policy. We urge scientists who develop monitoring programs to plan in advance to ensure high data quality, accessibility, and cost-effectiveness, and we urge government agencies and other funding institutions to make greater commitments to increasing the amount and long-term stability of funding for environmental monitoring programs.

The role of bedrock topography on subsurface storm flow

We conducted a detailed study of subsurface flow and water table response coupled with digital terrain analysis (DTA) of surface and subsurface features at the hillslope scale in Panola Mountain Research Watershed (PMRW), Georgia. Subsurface storm flow contributions of macropore and matrix flow in different sections along an artificial trench face were highly variable in terms of timing, peak flow, recession characteristics, and total flow volume. The trench flow characteristics showed linkages with the spatial tensiometer response defining water table development upslope. DTA of the ground surface did not capture the observed spatial patterns of trench flow or tensiometric response. However, bedrock surface topographic indices significantly improved the estimation of spatial variation of flow at the trench. Point-scale tensiometric data were also more highly correlated with the bedrock surface-based indices. These relationships were further assessed for temporal changes throughout a rainstorm. Linkages between the bedrock indices and the trench flow and spatial water table responses improved during the wetter periods of the rainstorm, when the hillslope became more hydrologically connected. Our results clearly demonstrate that in developing a conceptual framework for understanding the mechanisms of runoff generation, local bedrock topography may be highly significant at the hillslope scale in some catchments where the bedrock surface acts as a relatively impermeable boundary.

The role of event water, a rapid shallow flow component, and catchment size in summer stormflow

Seven nested headwater catchments (8 to 161 ha) were monitored during five summer rain events to evaluate storm runoff components and the effect of catchment size on water sources. Two-component isotopic hydrograph separation showed that event-water contributions near the time of peakflow ranged from 49% to 62% in the 7 catchments during the highest intensity event. The proportion of event water in stormflow was greater than could be accounted for by direct precipitation onto saturated areas. DOC concentrations in stormflow were strongly correlated with stream 18 O composition. Bivariate mixing diagrams indicated that the large event water contributions were likely derived from flow through the soil O-horizon. Results from twotracer, three-component hydrograph separations showed that the throughfall and O-horizon soil-water components together could account for the estimated contributions of event water to stormflow. End-member mixing analysis confirmed these results. Estimated event-water contributions were inversely related to catchment size, but the relation was significant for only the event with greatest rainfall intensity. Our results suggest that perched, shallow subsurface flow provides a substantial contribution to summer stormflow in these small catchments, but the relative contribution of this component decreases with catchment size. q 1999 Elsevier Science B.V. All rights reserved.

Effect of groundwater springs on NO3− concentrations during summer in Catskill Mountain streams

Groundwater and stream water data collected at three headwater catchments in the Neversink River watershed indicate that base flow is sustained by groundwater from two sources: a shallow flow system within the till and soil and a deep flow system within bedrock fractures and bedding planes that discharges as perennial springs. Data from eight wells finished near the till/bedrock interface indicate that saturated conditions are not maintained in the shallow flow system during most summers. In contrast, the discharge of a perennial spring remained constant during two summer rainstorms, providing evidence that the deep flow system is disconnected from the shallow flow system in summer. Discharge from perennial springs was the principal source of streamflow in a headwater reach during low flow. Mean NO3− concentrations were 20–25 μmol L−1 in five perennial springs during the summer but only 5–10 μmol L−1 in shallow groundwater. Thus the deep flow system does not reflect typical NO3− concentrations in the soil during summer. A hydrologic budget at a headwater drainage reveals that March and late fall are the principal groundwater recharge periods. Residence time modeling based on analyses of 18O and 35S indicates that groundwater in the deep flow system is 6–22 months old. These data indicate that summer base flow largely originates from previous dormant seasons when available soil NO3− is greater. In these Catskill watersheds, high base flow concentrations of NO3− during summer do not provide sufficient evidence that the atmospheric N deposition rate exceeds the demand of terrestrial vegetation.

Analysis of δ15N and δ18O to differentiate NO3− sources in runoff at two watersheds in the Catskill Mountains of New York

� of precipitation was � 0.2%, that of soil water was +1.4%, and that of stream water was +2.3%; these values showed greater overlap among the three different waters than did the d 18 O-NO3 � values, indicating that d 15 N-NO3 � was not as useful for source separation. Soil water d 18 O-NO 3 � values decreased, and d 15 N-NO3 values increased, from the O to the B and C horizons, but most of the differences among horizons were not statistically significant. Nitrate derived by nitrification in incubated soil samples had a wide range of d 15 N-NO3 � values, from +1.5% to +16.1%, whereas d 18 O-NO 3 � values ranged more narrowly, from +13.2% to +16.0%. Values of d 18 O-NO3 indicated that NO3 in stream water is mainly derived from nitrification. Only during a high-flow event that exceeded the annual flood was precipitation a major contributor to stream water NO3 . Values of d 18 O-NO3 and d 15 N-NO3 changed at differing rates as NO3 cycled through these watersheds because d 18 O-NO3 values change sharply through the incorporation of oxygen from ambient water and gas during nitrification, whereas d 15 N-NO3 values change only incrementally through fractionation during biocycling processes. The results of this study show that most NO3 is first cycled through the biota and nitrified before entering the stream. INDEX TERMS: 1040 Geochemistry: Isotopic composition/chemistry; 1615 Global Change: Biogeochemical processes (4805); 1803 Hydrology: Anthropogenic effects; 1806 Hydrology: Chemistry of fresh water; 1871 Hydrology: Surface water quality; KEYWORDS: nitrogen deposition, nitrogen saturation, nitrification, isotope, Catskill Mountains, snowmelt

Base cation concentrations in subsurface flow from a forested hillslope: The role of flushing frequency

A 20-m-wide trench was excavated to bedrock on a hillslope at the Panola Mountain Research Watershed in the Piedmont region of Georgia to determine the effect of upslope drainage area from the soil and bedrock surfaces on the geochemical evolution of base cation concentrations in subsurface flow. Samples were collected from ten 2-m sections and five natural soil pipes during three winter rainstorms in 1996. Base cation concentrations in hillslope subsurface flow were generally highest early and late in the storm response when flow rates were low, but during peak flow, concentrations varied little. Base cation concentrations in matrix flow from the 10 trench sections were unrelated to the soil surface drainage area and weakly inversely related to the bedrock surface drainage area. Base cation concentrations in pipe flow were lower than those in matrix flow and were also consistent with the inverse relation to bedrock surface drainage area found in matrix flow. The left side of the trench, which has the highest bedrock surface drainage area, had consistently lower mean base cation concentrations than the right side of the trench, which has the lowest bedrock surface drainage area. During moderate size rain events of about 20–40 mm, subsurface flow occurred only on the left side of the trench. The greater volume of water that has flowed through the left side of the trench appears to have resulted in greater leaching of base cations from soils and therefore lower base cation concentrations in subsurface flow than in flow from the right side of the trench. Alternatively, a greater proportion of flow that bypasses the soil matrix may have occurred through the hillslope on the left side of the trench than on the right side. Flushing frequency links spatial hillslope water flux with the evolution of groundwater and soil chemistry.

Retention of NO3- in an upland stream environment : A mass balance approach

AbstractModels of the effects of atmosphericN deposition in forested watersheds have notadequately accounted for the effects of aquatic andnear-stream processes on the concentrations and loadsof NO

Sources and transformations of nitrate from streams draining varying land uses: Evidence from dual isotope analysis

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