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The salinization of Mirror Lake in the White Mountains of New Hampshire has been ongoing steadily since Interstate 93 (I-93) was built through the NE subcatchment of the lake in the fall and winter of 1969–1970. Salt added to I-93 during winter as a deicer has been transported to the lake by different quantified, hydrologic pathways, but primarily from the Northeast Tributary, which was intersected by I-93. Now, surprisingly, after the New Hampshire Department of Transportation has spent more than $500,000 on recent structural modifications to divert salt from I-93 away from the Northeast subcatchment of Mirror Lake, applications of salt to a small, town road traversing the other two subcatchments for the lake and servicing a new housing development, have become the major source of salt to the lake. Streamflow from these two subcatchments currently provides more than three times as much salt to the lake as from I-93, and the salt concentration in the lake continues to rise. [ABSTRACT FROM AUTHOR]

Streamwater chemistry was measured at 100-m intervals in all streams of the Hubbard Brook Valley, NH during ‘spring’ (May–July) and during ‘fall’ (October–December) 2001. Overall, streamwater chemistry was very similar during these two periods, but fall median concentrations were consistently higher than spring values, except for ANC, pH, NO3 − and PO4 3−, which had lower values in fall. Median concentrations for NH4 + were approximately the same in spring and fall. Stream chemistry varied throughout the Hubbard Brook Valley by elevation, channel length, drainage area and type of drainage, but most of the variability in stream chemistry was subtle and relatively small. Overall, there were relatively large (two- to 10-fold) changes in chemistry with longitudinal distance of wetted channel, elevation and/or size of drainage area in some streams and for some elements (e.g., H+, Al n+, DOC), but other chemical concentrations changed relatively little (e.g., Cl−, dissolved Si). The main Hubbard Brook, a fifth-order stream at the mouth of the Valley, was remarkably constant in chemistry throughout its length, except where human disturbance near the mouth changed the chemistry. Differences in vegetation, geologic substrates and wetland areas were related to changes in pattern of streamwater chemistry throughout the Valley. [ABSTRACT FROM AUTHOR]

Chlorine is a minor constituent of most rocks and a minor (although essential) element in plants, but it cycles rapidly through the hydrosphere and atmosphere. In forest ecosystem studies, chloride ion (Cl−) is often thought to be conservative in the sense that the sources and sinks within the ecosystem are assumed negligible compared to inputs and outputs. As such, Cl− is often used as a conservative tracer to assess sources and transformations of other ions. In this paper we summarize research on chloride over the course of 36 years (1964–2000) at the Hubbard Brook Experimental Forest (HBEF) in central New Hampshire, USA. Evidence presented here suggests that in the 1960s and 1970s the dominant source of atmospheric Cl− deposition was from pollutant sources, probably coal burning. In the 1970s the Cl− inputs in bulk deposition declined, and the lower Cl− deposition in the last two decades is dominated by marine sources. Between 1964 and 2000 there was no significant trend in Cl− export in stream flow, thus the net hydrologic flux (NHF = bulk deposition inputs − streamflow outputs) has changed over this period. Early in the record the NHF was on average positive, indicating net retention of Cl− within the system, but since about 1980 the NHF has been consistently negative, indicating an unmeasured input or source within the ecosystem. Dry deposition can account for at least part of that unmeasured source, and it appears that release of Cl− from mineralization of soil organic matter (SOM) may also play an important role. We believe that accumulation of Cl− in vegetation during the 1960s and 1970s offset the unmeasured source and resulted in net ecosystem retention. Accumulation of vegetative biomass has ceased since about 1982, leading to the apparent net export (negative NHF) since that time. Although we have no direct measurements of Cl− accumulation in vegetation, our estimates suggest that an aggrading forest could sequester about 32 mol Cl ha−1 year−1, or about a third of the annual average bulk deposition flux to this ecosystem. Experimental additions of Cl− to the forest floor cause increases in Cl− concentration in foliage, throughfall, and soil solution. Manipulations of vegetation also affect the Cl− cycle. Harvesting or devegetation of watersheds causes an increase in the Cl− concentration and flux in stream water for several years after the disturbance. This period of release is followed by a period of reaccumulation of Cl− that may last more than 15 years. In this respect, the behavior of Cl− after disturbance parallels that of NO3−, for which export increases after disturbance due to reduced plant nitrogen uptake and mineralization of nitrogen from detritus, rather than SO42−, for which export decreases after disturbance due to pH-dependent adsorption onto mineral soils. The interannual pattern of Cl− export from the system primarily reflects the atmospheric inputs, but the net retention and cycling of Cl− within the system appears to be largely under biological, rather than geochemical, control. [ABSTRACT FROM AUTHOR]

Despite the widely recognized importance of disturbance in accelerating the loss of elements from land, there have been few empirical studies of the effects of natural disturbances on nitrogen (N) dynamics in forest ecosystems. We were provided the unusual opportunity for such study, partly because the intensively monitored watersheds at the Hubbard Brook Experimental Forest (HBEF), New Hampshire, experienced severe canopy damage following an ice storm. Here we report the effects of this disturbance on internal N cycling and loss for watershed 1 (W1) and watershed 6 (W6) at the HBEF and patterns of N loss from nine other severely damaged watersheds across the southern White Mountains. This approach allowed us to test one component of N limitation theory, which suggests that N losses accompanying natural disturbances can lead to the maintenance of N limitation in temperate zone forest ecosystems. Prior to the ice storm, fluxes of nitrate (NO3-) at the base of W1 and W6 were similar and were much lower than N inputs in atmospheric deposition. Following the ice storm, drainage water NO3- concentrations increased to levels that were seven to ten times greater than predisturbance values. We observed no significant differences in N mineralization, nitrification, or denitrification between damaged and undamaged areas in the HBEF watersheds, however. This result suggests that elevated NO3- concentrations were not necessarily due to accelerated rates of N cycling by soil microbes but likely resulted from decreased plant uptake of NO3-. At the regional scale, we observed high variability in the magnitude of NO3- losses: while six of the surveyed watersheds showed accelerated rates of NO3- loss, three did not. Moreover, in contrast to the strong linear relationship between NO3- loss and crown damage within HBEF watersheds [r2: (W1 = 0.91, W6 = 0.85)], stream water NO3- concentrations were weakly related to crown damage (r2 = 0.17) across our regional sites. The efflux of NO3- associated with the ice storm was slightly higher than values reported for soil freezing and insect defoliation episodes, but was approximately two to ten times lower than NO3- fluxes associated with forest harvesting. Because over one half of the entire year’s worth of N deposition was lost following the ice storm, we conclude that catastrophic disturbances contribute synergistically to the maintenance of N limitation and widely observed delays of N saturation in northern, temperate zone forest ecosystems. [ABSTRACT FROM AUTHOR]

Provides information on the water source to four U.S. wetlands. Hydrologic functions of lakes and wetlands in different hydrogeologic functions and climatic settings; Interaction of surface water and ground water; Comparisons of the water balances of the four wetlands.

From 1978 through 1989, a wet-only precipitation collector operated for the National Atmospheric Deposition Program, an independent wet-only collector, and a bulk precipitation collector were co-located at the Hubbard Brook Experimental Forest (HBEF) in central New Hampshire. A second bulk precipitation collector was maintained at another location within the HBEF. There were statistically significant differences between the chemistry from co-located wet-only collections for Ca2+, K+, NH4+, pH, and NO3-. The differences for K+ and pH though statistically significant were very small but consistant. The differences for Ca2+ were related to early contamination problems, and differences in NH4+ and NO3- were related to episotic events. Bulk precipitation was significantly richer in K+ than wet-only precipitation. There were no differences for any ions between the bulk collections at the two locations. While there were minor differences, after 1981 when the contamination problems had been resolved, data from all collectors at all locations adequately characterized the precipitation chemistry of the site. [ABSTRACT FROM AUTHOR]

Annual, volume-weighted concentrations of SO42- in bulk precipitation have declined steadily (?0.44 ?u mol/liter-yr) since 1965 at the Hubbard Brook Experimental Forest (HBEF), NH in response to decreases in regional SO2 emissions (r2 = 0.74). Similar declines in concentrations have occurred in wet-only precipitation at HBEF and at nearby sites since 1978. However, decreases in SO42- concentrations following passage of the U.S. Clean Air Act Amendments in 1990, were not unusual from the perspective of long-term data from the HBEF. Statistically significant declines (?5.6 mol/ha-yr) in bulk deposition of SO42- also have occurred since 1965 in relation to decreases in SO2 emissions (r2 = 0.58), but annual variations in deposition also are strongly related to amount of precipitation and other factors. [ABSTRACT FROM AUTHOR]

Relatively high deposition of nitrogen (N) in the northeastern United States has caused concern because sites could become N saturated. In the past, mass-balance studies have been used to monitor the N status of sites and to investigate the impact of increased N deposition. Typically, these efforts have focused on dissolved inorganic forms ofN (DIN = NH4-N + NO3-N) and have largely ignored dissolved organic nitrogen (DON) due to difficulties in its analysis. Recent advances in the measurement of total dissolved nitrogen (TDN) have facilitated measurement of DON as the residual of TDN - DIN.We calculated DON and DIN budgets using data on precipitation and streamwater chemistry collected from 9 forested watersheds at 4 sites in New England. TDN in precipitation was composed primarily of DIN. Net retention of TDN ranged from 62 to 89% (4.7 to 10 kg ha-1 yr -1) of annual inputs. DON made up the majority of TDNin stream exports, suggesting that inclusion of DON is critical to assessing N dynamics even in areas with large anthropogenic inputs of DIN. Despite the dominance of DON in streamwater, precipitation inputs of DON were approximately equal to outputs. DON concentrations in streamwater did not appear significantly influenced by seasonal biological controls, but did increase with discharge on some watersheds. Streamwater NO3-N was the only fraction of N that exhibited a seasonal pattern, with concentrations increasing during the winter months and peaking during snowmelt runoff. Concentrations of NO3-N varied considerably among watersheds and are related to DOC:DON ratios in streamwater. Annual DIN exports were negatively correlated with streamwater DOC:DON ratios, indicating that these ratios might be a useful index of N status of upland forests. [ABSTRACT FROM AUTHOR]