Changes In Stream Water Chemistry Research Articles

Reversal of acidification in tributaries of the River Duddon (English Lake District) between 1970 and 1998

Long-term changes in stream water chemistry in the upper Duddon catchment (southwest Lake District, UK) were investigated. Ten streams were sampled and analysed weekly during 1998, and the results compared with data for the early 1970s and 1986. The waters exhibited a range of pH, average values for 1998 being 5.04–7.04. For all the streams, the average pH in 1998 was greater than that during 1971–73. Statistical analysis was carried out, using the 1970s data to estimate the magnitude of inter-annual variation, and taking discharge into account on the basis of antecedent rainfall. The results showed that for two of the streams the pH increase was significant at the 2.5% level, while for a further three it was significant at the 10% level. Comparison of the 1998 concentrations of nitrate and non-marine sulphate with data obtained for five streams in 1973–74 showed that average nitrate concentration had increased from 11 to 20 μeq dm −3 while that of non-marine sulphate had decreased from 94 to 50 μeq dm −3. For four of the streams, comparisons were also made between the 1998 data and those for 1986. In three cases, pH in 1998 was generally higher, and Al generally lower, than the values for 1986, but in the fourth case little difference was evident. The present results support observations for five nearby standing waters, strengthening the evidence for a general reversal of acidification in the southwest part of Lake District, due to a decline in the deposition of pollutant sulphur.

Changes in streamwater chemistry after 20 years from forested watersheds in New Hampshire, U.S.A.

Changes in streamwater chemistry after 20 years from forested watersheds in New Hampshire, U.S.A.

Seasonal change in precipitation, snowpack, snowmelt, soil water and streamwater chemistry, northern Michigan

We have studied weekly precipitation, snowpack, snowmelt, soil water and streamwater chemistry throughout winter for over a decade in a small (176 ha) northern Michigan watershed with high snowfall and vegetated by 60 to 80 year-old northern hardwoods. In this paper, we examine physical, chemical, and biological processes responsible for observed seasonal change in streamwater chemistry based upon intensive study during winter 1996-1997. The objective was to define the contributions made to winter and spring streamwater chemical concentration and flux by processes as snowmelt, over-winter forest floor and surface soil mineralization. immobilization, and exchange, and subsurface flowpath. The forest floor and soils were unfrozen beneath the snowpack which permitted most snowmelt to enter. Over-winter soil mineralization and other biological processes maintain shallow subsurface ion and dissolved organic carbon (DOC) reservoirs. Small, but steady, snowmelt throughout winter removed readily mobilized soil NO 3 - which resulted in high over-winter streamwater concentrations but little flux. Winter soil water levels and flowpaths were generally deep which increased soil water and streamwater base cation (C B ), HCO 3 - , and Si concentrations. Spring snowmelt increased soil water levels and removal of ions and DOC from the biologically active forest floor and shallow soils. The snowpack solute content was a minor component in determining streamwater ion concentration or flux during and following peak snowmelt. Exchangeable ions, weakly adsorbed anions, and DOC in the forest floor and surface soils dominated the chemical concentration and flux in soil water and streamwater. Following peak snowmelt, soil microbial immobilization and rapidly increased plant uptake of limiting nutrients removed nearly all available nitrogen from soil water and streamwater. During the growing season high evapotranspiration increased subsurface flowpath depth which in turn removed weathering products, especially C B , HCO 3 - , and Si, from deeper soils. Soil water was a major component in the hydrologic and chemical budgets.

A regional application of the MAGIC model in Wales: calibration and assessment of future recovery using a Monte-Carlo approach

Abstract. A survey and resurvey of 77 headwater streams in Wales provides an opportunity for assessing changes in streamwater chemistry in the region. The Model of Acidification of Groundwater In Catchment (MAGIC) has been calibrated to the second of two surveys, taken in 1994-1995, using a Monte-Carlo methodology. The first survey, 1983-1984, provides a basis for model validation. The model simulates a significant decline of water quality across the region since industrialisation. Agreed reductions in sulphur (S) emissions in Europe in accordance with the Second S Protocol will result in a 49% reduction of S deposition across Wales from 1996 to 2010. In response to these reductions, the proportion of streams in the region with mean annual acid neutralising capacity (ANC) > 0 is predicted to increase from 81% in 1995 to 90% by 2030. The greatest recovery between 1984 and 1995 and into the future is at those streams with low ANC. In order to ensure that streams in the most heavily acidified areas of Wales recover to ANC zero by 2030, a reduction of S deposition of 80-85% will be required.

The hydrochemistry of the headwaters of the River Severn, Plynlimon

Abstract. Water quality data spanning 13 years and covering an extensive range of major, minor and trace elements in rain and stream waters at Plynlimon in mid Wales, are presented. Rainfall water chemistry is highly variable due to varying proportions of marine and pollutant derived constituents associated with patterns of atmospheric circulation. Stream waters, being composed of different proportions of waters from three chemically distinct sources at any one time (atmospheric deposition, the soil system and deeper groundwaters), are also chemically highly variable. For example, components predominantly derived from deposition such as chloride change only in response to sea-salt deposition episodes. Solutes associated with bedrock weathering such as calcium, magnesium, and alkalinity decrease with increasing flow, those associated with the upper soil layers such as aluminium, many transition metals, dissolved organic carbon and hydrogen ions increase with increasing flow. The nutrients (e.g. nitrate, boron, bromide and iodine) exhibit strong seasonal cycles associated with cycles of vegetation growth and decay. The changes in stream water chemistry resulting from tree harvesting in the Afon Hore catchment are shown to have run their course within a period of eight years. Nutrient increases in the first few years following the commencement of felling have returned to or fallen below pre-felling values. Aluminium changes are shown to be complicated by changes in nitrate and calcium. Aluminium concentrations initially increased and have fallen below their pre-felling value. Data for chloride suggest a reduction in capture of dry and mist deposition; this indicates the importance of understanding reduced deposition as a result of felling. Felling has also affected the soil micro-climate which experiences greater fluctuations in temperature and an increase in the concentration of constituents associated with organic matter. Input-output mass balance estimates show that atmospheric inputs of many constituents are retained strongly by the catchment (e.g. ammonium, phosphate, barium, boron, lead and iodine). In contrast, many of the transition elements as well as divalent base cations, aluminium and alkalinity show a net release from the catchment. Conservative constituents such as chloride and sodium show a net input-output balance.

The influence of parent material on small-scale spatial changes in streamwater chemistry in Scottish upland catchments

Spatial changes in streamwater chemistry in seven upland catchments in NE Scotland have been studied using samples collected at 250 m intervals from the stream source to the catchment outlet. The catchments contain a number of different parent materials including granites and diorite from the Lochnagar Complex, and metasediments and metabasites from the Argyll and Appin Groups of the Dalradian Supergroup. Samples were collected under low flow conditions between June 1989 and January 1990 and ten component ions were determined; this paper concentrates on pH, Ca, Mg, Na and K. All seven catchments show major changes in stream solute concentrations along their length. Samples collected immediately downstream of the source typically show a rapid increase in pH with distance, reflecting degassing in the stream of CO 2 from the soil solution. Further down the catchment small-scale spatial changes in streamwater chemistry appear to be strongly influenced by the underlying geology. As the stream flows over parent materials with distinctly different geochemical characteristics, the pH, and Ca and Mg concentrations in the stream show rapid changes, reflecting changes in the underlying lithology. In a number of the catchments K also exhibits significant spatial variability along the length of the stream. The underlying geology appears to have little effect on Na concentrations, which typically increase from the source to the bottom of the catchment. These data suggest that small-scale spatial changes in streamwater chemistry may provide a useful tool for identifying changes in the underlying geology in poorly exposed areas. In addition, they also have implications for regional critical load mapping and prediction of streamwater sensitivity to acidification.

Evaluation of the use of soil ion exchange properties for predicting streamwater chemistry in upland catchments

The potential of soil ion exchange chemistry for predicting streamwater quality is evaluated using soil and streamwater chemical data from ten upland catchments in NE Scotland. The study catchments vary from those dominated by acid hill peats, alpine soils and podzols to those dominated by more base-rich soils, including cambisols and gleysols. Soil and streamwater chemical data combined with precipitation and parent material chemistry are also used to investigate sources and pathways of water movement. In all soils studied, Ca and Mg are the dominant exchangeable base cations in the surface soil horizons. In most soils, Na becomes increasingly important on the exchange complex with depth down the soil profile. Plots of the relative proportions of Na:Ca:Mg in streamwater show that, during periods of high discharge, streamwater chemistry tends to become relatively more Na-rich compared with Ca and Mg. Using triangular diagrams, streamwater chemistry can be described as a mixture of geochemically distinct packages of water derived from precipitation inputs, specific parent materials and key soil horizons, although spatially important soils within catchments may be relatively unimportant in controlling streamwater chemistry. Changes in streamwater chemistry at high flow can be explained by dilution of water derived from groundwater sources or the B/C horizon, either with laterally flowing water from the upper soil horizons, or with precipitation. In conclusion, changes in the relative proportions of Na:Ca:Mg in streamwater during storms suggest that precipitation chemistry may play a greater role than hitherto suggested in modifying solute chemistry during periods of high flow.

Randomized intervention analysis of the response of the West Bear Brook Watershed, Maine to chemical manipulation

A paired watershed manipulation study was conducted to study the qualitative and quantitative impacts of elevated acidic precipitation on the chemistry of soils, soil water, and stream water. The Bear Brook Watershed, Maine (BBWM) is drained by two first order streams, East Bear Brook and West Bear Brook. The streams were chemically and hydrologically monitored for two years (1987-1989) and exhibited similar behavior. The West Bear watershed was then chemically manipulated with the bimonthly addition of (NH4)2SO4 (150 mol ha-1 per application). To assess whether changes in stream water chemistry occurred following the chemical manipulation, and if so when, Randomized Intervention Analysis (RIA) was performed using time-paired data from the two watersheds. RIA, along with autocorrelation analysis, statistically evaluates the behavior of the various analytes under the influence of artificial acidification and therefore provided an objective basis for determining whether changes in the geochemical behavior of West Bear Brook were temporally associated with the chemical manipulation. RIA analysis using weekly data yielded higher probabilities of stream water chemistry effects being temporally linked with the manipulation than RIA analysis using monthly data. Using monthly data, there is a lower probability that short-term excursions in water chemistry related to hydrology can be detected. According to RIA analysis of weekly data for three years of manipulation (1989-1992), the statistically-determined order of impact on water chemistry was (K+, Mg2+, Na+, Ca2+, total Al, PH, SO 4 2- , NO 3 - , DOC) > Si > Cl-Autocorrelation analysis indicated that several analytes exhibited increasingly deterministic behavior, including SO 4 2- , base cations, and DOC. Both RIA and autocorrelation analysis indicated no temporal relationship between the manipulation and hydrology.

Importance of surface‐subsurface exchange in stream ecosystems: The hyporheic zone

In many streams, significant amounts of water are exchanged between saturated sediments surrounding the open channel (the hyporheic zone) and the channel itself. Such exchanges with the hyporheic zone have the potential to cause large changes in streamwater chemistry because the rates of biogeochemical processes and the actual types of processes (e.g. anaerobic vs. aerobic metabolism) may be fundamentally different. I propose an organizational scheme for grouping stream systems into clusters of minimal, moderate, and maximal contribution of hyporheic metabolism to the overall ecosystem. Lack of information on quantitative hydrology for different stream systems prohibits actual testing of this framework. An alternative scheme is presented that organizes several well‐studied streams as a function of subsurface residence time and differences in oxygen content. This second scheme is intended to stimulate discussion of conceptual frameworks for cross‐system comparisons of the importance of hyporheic sediments in stream ecosystems.

Modelling streamwater chemistry as a mixture of soilwater end-members — A step towards second-generation acidification models

In present acidification models, soilwater characteristics, though modelled, are seldom checked against field observations. Given that such data are now collected as part of many catchment studies, a technique is developed whereby stream water can be predicted as a mixture of the observed soilwater classes or end-members. Provided that a sufficient set of end-members has been identified, a least-squares technique can be used to estimate the contribution to the stream from each end-member, whenever streamwater samples have been taken. For two catchments, Birkenes in southern Norway and Plynlimon in Mid-Wales, the analysis indicates that the soilwater end-members observed to date are insufficient to explain streamwater chemistry. However, properties of the missing soil waters have been identified, thus facilitating future field work. When an adequate set of soilwater end-members has been established, long-term predictions of changes in streamwater chemistry reduce to the problem of predicting the fate of each end-member. Thus, a separate hydrological submodel is not needed, since the mixing patterns are derived from the end-member analysis.

A model of surface water acidification in Cumbria and its uses in long‐term research

SUMMARY. 1. A description is given of a simple process‐based model of deposition‐catchment interactions in areas of Cumbria underlain by rocks of the Borrowdale Volcanic Series. The processes considered are evapotranspiration, nitrogen uptake by plants, dissolution and precipitation of A1(OH)3, basecation weathering, hydrolysis of Al3+, reactions of the carbonate system, and water flow routing. Model parametersare estimated from 1980s data for deposition and streamwater chemistry. It is shown that the‐ model is also applicable to tarns (small lakes). Analysis of 1970s streamwater data highlights uncertainties about deposition concentrations of NH4+ and catchment transformations of nitrogen.2. Using estimates of past deposition compositions, past compositions of tarn waters are estimated and indicate declines in pH I of up to 1 unit between c. 1850 and c, 1950, These changes are similar to those estimated independently from analysis of sediment diatoms. The model also shows that the historical pH trends are consistent with other paiaeolimnological evidence that Cumbrian soils have been acid for several thousand years. The model output is also consistent with direct evidence suggesting that the chemical compositions of Cumbrian tarns have altered little during the past 30 years.3. The model is used to estimate water compositions during high‐flow episodes at various times in the past, and shows that even a small increase in depositional acidity would have made high‐flow waters sufficiently acid and aluminum‐rich to limit faunal abundance. This is consistent with the limited amount of observational evidence that is available.4. The model can be used (a) for prediction, given scenarios for future deposition compositions or catchment behaviour, and (b) as a framework for planning future studies and interpreting data. Further work on the model should improve the reliability of its parameters, find better descriptions of processes dealt with in the current version, and introduce processes currently ignored. The present analysis indicates that fieldwork is needed to study nitrogen transformations, soil properties and biological responses to changes in streamwater chemistry.

Atmospheric deposition effects on the chemistry of a stream in Northeastern Georgia

The quantity and quality of precipitation and streamwater were measured from August 1985 through September 1986 in the Brier Creek watershed, a 440-ha drainage in the Southern Blue Ridge Province of northeastern Georgia, to determine stream sensitivity to acidic deposition. Precipitation samples collected at 2 sites had a volume-weighted average pH of 4.40 whereas stream samples collected near the mouth of Brier Creek had a discharge-weighted average pH of 6.70. Computed solute fluxes through the watershed and observed changes in streamwater chemistry during storm flow suggest that cation exchange, mineral weathering, SO42− adsorption by the soil, and groundwater discharge to the stream are probable factors affecting neutralization of precipitation acidity. Net solute fluxes for the watershed indicate that, of the precipitation input, > 99% of the H+, 93% of the NH4+ and NO3−, and 77% of the SO42− were retained. Sources within the watershed yielded base cations, Cl−, and HCO3− and accounted for 84, 47, and 100% of the net transport, respectively. Although streamwater SO42− and NO3− concentrations increased during stormflow, peak concentrations of these anions were much less than average concentrations in the precipitation. This suggests retention of these solutes occurs even when water residence time is short.

Nutrient dynamics of forested catchments in Southeastern Australia and changes in water quality and nutrient exports following clearing

Nutrient inputs in rainfall, and streamwater chemistry and quality, were measured from May 1976 to April 1982 at three forested catchments in Victoria. Streamwater chemistry was influenced by the strong seasonal fluctuations in streamflow. Yearly input-export balances for Na, K, Ca, Mg and Cl varied substantially and were highly correlated with runoff. This underlines the importance of sampling a wide range of climatic variation to derive meaningful balances. Calibration relationships between catchments were used to evaluate the impact of clearing native eucalypt forest for the establishment of P. radiata on streamwater chemistry and quality and on nutrient exports. Clearing was found to have little effect on streamwater quality, thus demonstrating the effectiveness of a 30-m wide buffer strip retained on both sides of the stream channel. Only minor changes in streamwater chemistry were observed; however, exports of nutrients and suspended solids were significantly higher because of increased discharge following clearing. Exports of most nutrients returned to pre-treatment levels within 18 months after clearing. Nutrient losses in streamwater were small when compared with losses due to burning the cleared vegetation. Balances for Na were used to estimate nutrient inputs from geological weathering. It was concluded that inputs of Ca are probably too low to ensure adequate supply of Ca for successive rotations of P. radiata, and future management practices should aim at conserving this nutrient.

Predicted changes in streamwater chemistry following reduced/increased sulphur deposition using the ?Birkenes model?

A sensitivity analysis of some important parameters in a mathematical model previously found to reproduce major short-term variations in water chemistry in some streams, has been carried out. The results are also relevant in a discussion of possible changes in stream acidity for changes in S deposition. In the simulations sulphate concentrations in streamwater were doubled or halved compared to present day values. Assuming no change in the lime potential of the soil, the peak acidity during snowmelt changed with up to 0.9 pH units; shifts from 0.4 to 0.5 units occurred in many cases. By simultaneously changing the sulphate stream concentration and the lime potential with 0.2 units shifts of about 1 pH unit were obtained in the simulations for some acidity peaks.

Clearcutting and the Biogeochemistry of Streamwater in New England

Abstract A survey shows that clearcutting in New England may increase stream nutrients, including nitrate-nitrogen, calcium, and potassium. The largest increases were found in northern hardwoods in New Hampshire. Stream insect populations, particularly mayflies and true flies, increased in clearcuts in response to increased stream temperature, algal populations, and organic matter. Changes in streamwater chemistry and biology indicate that clearcutting forestlands does affect streams throughout New England. However, the magnitude of differences is such that if erosion and sedimentation are controlled, clearcutting as practiced by foresters today does not drastically change streamwater chemistry or biology.