Changes In Stream Water Chemistry Research Articles

Long‐term changes in stream water chemistry in small forested watersheds in the northern Kanto region

AbstractConcerns have been raised regarding the degradation of stream water quality due to the excessive influx of atmospheric deposition. This study aimed to reveal the long‐term variation in stream water chemistry in approximately 40 forested small watersheds in the northern Kanto region, based on 3 surveys conducted in 1991–1992, 2006–2007, and 2022. The factors influencing each dissolved element were investigated. Regarding long‐term variations in stream water chemistry, relatively stable concentrations of cations (Ca2+, Mg2+, K+, and Na+) and SiO2 were observed. However, the concentrations of anions (Cl−, , and ) decreased due to the improvement in the atmospheric environment and the diminishing effect of fertilization. Furthermore, the recent increase in stream water pH was attributed to an increase in bicarbonate (), compensating for the decrease in anion concentrations relative to cations. Geology was the most significant factor for inter‐watershed variations in cations and SiO2, and this influence remained relatively constant over 30 years. Forest practices, especially fertilization, had a significant effect on Cl− and , and contributed to higher concentrations in the fertilized watersheds than in the non‐fertilized watersheds over the 15 years following fertilization. Sulfate deposition was a significant influencing factor for , and the concentration fluctuated under long‐term variations in deposition over the past 30 years. Despite substantial acid deposition in the study area, the absence of stream water acidification could be attributed to the abundant cation supply from bedrock and volcanic ash, which underwent weathering processes.

Freshwater salinization syndrome limits management efforts to improve water quality.

Freshwater Salinization Syndrome (FSS) refers to groups of biological, physical, and chemical impacts which commonly occur together in response to salinization. FSS can be assessed by the mobilization of chemical mixtures, termed "chemical cocktails", in watersheds. Currently, we do not know if salinization and mobilization of chemical cocktails along streams can be mitigated or reversed using restoration and conservation strategies. We investigated 1) the formation of chemical cocktails temporally and spatially along streams experiencing different levels of restoration and riparian forest conservation and 2) the potential for attenuation of chemical cocktails and salt ions along flowpaths through conservation and restoration areas. We monitored high-frequency temporal and longitudinal changes in streamwater chemistry in response to different pollution events (i.e., road salt, stormwater runoff, wastewater effluent, and baseflow conditions) and several types of watershed management or conservation efforts in six urban watersheds in the Chesapeake Bay watershed. Principal component analysis (PCA) indicates that chemical cocktails which formed along flowpaths (i.e., permanent reaches of a stream) varied due to pollution events. In response to winter road salt applications, the chemical cocktails were enriched in salts and metals (e.g., Na+, Mn, and Cu). During most baseflow and stormflow conditions, chemical cocktails were less enriched in salt ions and trace metals. Downstream attenuation of salt ions occurred during baseflow and stormflow conditions along flowpaths through regional parks, stream-floodplain restorations, and a national park. Conversely, chemical mixtures of salt ions and metals, which formed in response to multiple road salt applications or prolonged road salt exposure, did not show patterns of rapid attenuation downstream. Multiple linear regression was used to investigate variables that influence changes in chemical cocktails along flowpaths. Attenuation and dilution of salt ions and chemical cocktails along stream flowpaths was significantly related to riparian forest buffer width, types of salt pollution, and distance downstream. Although salt ions and chemical cocktails can be attenuated and diluted in response to conservation and restoration efforts at lower concentration ranges, there can be limitations in attenuation during road salt events, particularly if storm drains bypass riparian buffers.

Circulation patterns of biogenic ions in Young Glacial areas.

The paper focuses on the effect of ponds (geographically isolated wetlands) on water quality within internally drained areas in a river catchment. The important part of the study was the point of formation of a periodic hydrographic network of internally drained areas linked with a main river as well as the identification of the circulation pattern of ions in such a system. The aim of the study was to examine the extent to which ponds pollute the main river upon physical connection with it. Research has shown that ponds participate actively in material circulation-including that of water and biogenic ions. The hydrographic network in Young Glacial areas is subject to very large seasonal changes. In the study area, the total length of the stream network in the dry season equaled 12 km, while in the wet season almost 75 km. At the same time, almost 50% of the internally drained areas in the catchment became connected with the surface runoff network. Such large seasonal changes in the hydrographic network yield large changes in stream water chemistry. In the study area, only 6 ponds were linked to the stream network during the dry season, while in the wet season, this number increased to 125. The parts of catchments featuring the largest changes in the hydrographic network as well as the largest number of ponds temporarily linked with surface runoff networks were characterized by a high content of total nitrogen and phosphorus-up to 244.2 kg N km2 per month and 26.2 kg P km2 per month.

Do stream water solute concentrations reflect when connectivity occurs in a small, pre-Alpine headwater catchment?

Abstract. Expansion of the hydrologically connected area during rainfall events causes previously disconnected areas to contribute to streamflow. If these newly contributing areas have a different hydrochemical composition compared to the previously connected contributing areas, this may cause a change in stream water chemistry that cannot be explained by simple mixing of rainfall and baseflow. Changes in stormflow composition are, therefore, sometimes used to identify when transiently connected areas (or water sources) contribute to stormflow. We identified the dominant sources of streamflow for a steep 20 ha pre-Alpine headwater catchment in Switzerland and investigated the temporal changes in connectivity for four rainfall events based on stream water concentrations and groundwater level data. First, we compared the isotopic and chemical composition of stormflow at the catchment outlet to the composition of rainfall, groundwater and soil water. Three-component end-member mixing analyses indicated that groundwater dominated stormflow during all events, and that soil water fractions were minimal for three of the four events. However, the large variability in soil and groundwater composition compared to the temporal changes in stormflow composition inhibited the determination of the contributions from the different groundwater sources. Second, we estimated the concentrations of different solutes in stormflow based on the mixing fractions derived from two-component hydrograph separation using a conservative tracer (δ2H) and the measured concentrations of the solutes in baseflow and rainfall. The estimated concentrations differed from the measured stormflow concentrations for many solutes and samples. The deviations increased gradually with increasing streamflow for some solutes (e.g. iron and copper), suggesting increased contributions from riparian and hillslope groundwater with higher concentrations of these solutes and thus increased hydrological connectivity. The findings of this study show that solute concentrations partly reflect the gradual changes in hydrologic connectivity, and that it is important to quantify the variability in the composition of different source areas.

Stream water quality in relation to watershed‐scale practical forest management in a cool‐temperate natural forest in northern Japan

AbstractThe water chemistry of a stream reflects the biogeochemical processes occurring in upstream forests. Anthropogenic disturbances in forests, such as cutting trees, altering the nitrogen (N) cycle, and increase in N leaching from the soil to streams, potentially cause acidification or eutrophication downstream. In forests with dense understory vegetation, mechanical site preparation following tree cutting is commonly used to improve the early establishment of tree seedlings. In cool‐temperate forests in northern Hokkaido, Japan, dense understory vegetation (mainly comprising Sasa dwarf bamboo) inhibits forest regeneration after tree cutting. Soil scarification is a common site preparation technique for eliminating Sasa bamboo and improving forest regeneration. Long‐term data are useful for examining the temporal changes in stream water chemistry exposed to different specific forest management practices under changing environment (e.g., climate change and atmospheric N deposition). For 14 years (2003–2016), we observed the stream water chemistry in naturally forested watersheds and at one point after the confluence of all streams in Uryu Experimental Forest of Hokkaido University (North Hokkaido Experimental Forests Site of JaLTER) in northern Japan. We also monitored stream discharge, water level and stream water temperature in each watershed. Water samples were collected from the outlets of 10 watersheds. The forest management practice in each watershed includes clear‐cutting, soil scarification in sparse forest with dense understory Sasa, and clear‐cutting and soil scarification followed by soil replacement. Long‐term data in the six unmanaged watersheds are also valuable as a background information to analyze the effect of long‐term climate, environment and vegetation changes on stream water chemistry. The measured water quality data of 1,873 water samples include the ion concentrations (Cl−, NO3−, SO42−, Na+, NH4+, K+, Mg2+, and Ca2+), pH, and electrical conductivity (EC) in the stream water. The range of the concentrations of Cl−, NO3−, SO42−, Mg2+, and Ca2+ in the stream water across all the watersheds throughout the observed periods (minimum to maximum) were 3.35–23.67, 0.01–8.68, 0.83–4.01, 0.45–2.55 and 0.72–6.16 mg L−1, respectively. Similarly, the stream pH and EC ranged from 6.04 to 7.53 and 3.14 to 9.47 mS m−1, respectively.The complete data set for this abstract published in the Data Paper section of the journal is available in electronic format in MetaCat in JaLTER at http://db.cger.nies.go.jp/JaLTER/metacat/metacat/datapaper%202020‐04.1/jalter‐en. [Correction added on 7 September 2020, after first online publication: JaLTER URL has been updated.]

Trends in surface water chemistry in afforested Welsh catchments recovering from acidification, 1991–2012

A key criterion of the UK Government's policy on sustainable forest management is safeguarding the quality and quantity of water. Forests and forestry management practices can have profound effects on the freshwater environment. Poor forest planning or management can severely damage water resources at great cost to other water users; in contrast good management that restores and maintains the natural functions of woodland can benefit the whole aquatic ecosystem.Forests and forest management practices can affect surface water acidification. Monitoring of water chemistry in ten forest and two moorland acid-sensitive catchments in upland Wales commenced in 1991. The streams were selected to supplement the United Kingdom Upland Waters Monitoring Network (UWMN) with additional examples of afforested catchments. Analysis of 22 years of water chemistry data revealed trends indicative of recovery from acidification. Excess sulphate exhibited a significant coherent decline, accompanied by increases in pH and “charge-balance based” acid neutralising capacity (CB-ANC). Alkalinity and “alkalinity-based” acid neutralising capacity (AB-ANC) exhibited fewer trends, possibily due to the variable responses of the organic - carbonate species to increasing pH in these low alkalinity streams. Whilst total anthropogenic acidity declined, dissolved organic carbon and Nitrate-Nitrogen (NNO3) concentrations have risen, and the contribution of NNO3 to acidification has increased.Between-stream variability was analysed using Principal Component Analysis of the trend slopes. Hierarchical clustering of the changes in stream water chemistry indicated three distinct clusters with no absolute distinction between moorland and forest streams. Redundancy analysis was used to test for significant site-specific variables that explained differences in the trend slopes, with rainfall, crop age, base cation concentration and forest cover being significant explanatory variables.

The effects of elevated atmospheric CO2 on freshwater periphyton in a temperate stream

This study examines the effects of elevated CO2 on the benthic biology of a temperate freshwater stream. We tested the hypotheses that elevated CO2 would increase periphyton biomass, alter elemental composition, and change community composition by increasing the frequency of algal taxa most limited by CO2 availability. Carbon dioxide was bubbled into reservoirs of stream water, increasing the ambient pCO2 by approximately 1100 ppm. The CO2-enriched water then flowed into artificial stream channels. Ceramic tiles were placed into the channels to allow for periphyton colonization. Dissolved inorganic carbon increased and pH decreased with added CO2. Measurements of biological parameters including periphyton biomass, algal C:N:P ratios, and community composition suggest that the periphyton were unaffected by the changes in stream water chemistry. We infer that rising atmospheric CO2 will impact stream water chemistry but that periphyton may not be the first to respond to these changes. Impacts to alkaline freshwater streams from elevated CO2 initially may be due to changes to terrestrial inputs that affect microbial decomposition and grazer activity, rather than through increases in periphyton carbon fixation. However, environmental characteristics of freshwater systems vary considerably, and additional studies are needed for accurate predictive modeling and monitoring of the effects of increasing atmospheric CO2 on freshwater streams.

Analysis of changes in stream water chemistry following forest management practices in Darabkola forest

Yol yapimi ve surutme gibi orman yonetimi uygulamalari buyuk olcude suyun kalitesini degistirebilir. Bu arastirmanin ana bakis acisi, surutme faaliyetleriyle gecirilen zamanin akarsu su kalite parametreleri uzerine etkisidir. Alti adet menfez, bu calisma icin kalici mesafeli yollarda uc tekrarlamali olarak uygulanmistir. Su ornekleri siselenerek toplanmistir. Butun ornekler soguk muhafaza edilerek; toplam askida kati madde (AKM), NO3 - ve PO4 -3 icin analiz edilmistir. T-testi sonuclari NO3 - ve PO4 -3 konsantrasyonlarinin anlamli derecede yuksek degerlerde (p

Importance of frequent storm flow data for evaluating changes in stream water chemistry following clear-cutting in Japanese headwater catchments

This study investigated the changes in stream water chemistry during low flow and storm flow following clear-cutting in a paired forest catchments. Regular grab samples, obtained mainly during low flow, showed that the Cl − concentration in stream water decreased, the NO 3 - concentration increased, and the Na +, SO 4 2 - , K +, Mg 2+, and Ca 2+ concentrations did not change significantly after clear-cutting. Highly frequent samplings revealed that solute concentrations at high flow changed to a larger degree after cutting than those at low flow. The NO 3 - concentration at high flow changed earlier and to a greater degree than that at low flow. In addition, Na +, K +, and Ca 2+ also increased at high flow just after clear-cutting, in association with NO 3 - flushing. The mean annual NO 3 - export after clear-cutting, as estimated by the highly frequent samplings including concentrations during storm flow, was more than 60 kg ha −1 and 1.5-fold higher than that calculated by only weekly sampling data. The largest difference was found 8 months after clear-cutting, when the methods differed by 40 kg ha −1 yr −1 and the estimate by the regular measurements with high-frequency sampling data was three-fold higher than that with the weekly regular sampling. These results show that high-frequency observation following forest cutting is important for accurate estimation of output fluxes.

Drivers and evolution of episodic acidification at the Bear Brook Watershed in Maine, USA

Despite decades of research about episodic acidification in many regions of the world, the understanding of what controls the transient changes in stream water chemistry occurring during rain and snow melt events is still limited. Here, we use 20 years of hydrological and stream chemical data from the paired watershed study at Bear Brook Watershed in Maine (BBWM), USA to improve the understanding of the effects of acid deposition on the causes, drivers, and evolution of episodic acidification. The long-term experimental study at BBWM includes 18 years of chemical treatment of the West Bear Brook (WB) watershed with (NH(4))(2)SO(4). East Bear Brook (EB) serves as reference. The treatment started in 1989 following a 2-year pretreatment period. We analyzed 212 hydrological episodes using an episode model that can separate and quantify individual drivers of the transient change in acid-neutralizing capacity (ANC) during hydrological events. The results suggest that 18 years of N and S addition have not affected the natural drivers of episodic acidification of base-cation dilution, marine sea salt episodes, or organic acidity during rain and snow melt events. The contribution of SO4(2-) to the ANC decline in WB has been increasing linearly since the beginning of watershed treatment, while the role of NO3- has remained relatively constant after an initial increase. This is contradictory to many previous shorter-term studies and illustrates the need for a more mechanistic understanding of the causes and drivers of episodic acidification during rain- and snow melt-driven hydrological events.

Investigating the applicability of end‐member mixing analysis (EMMA) across scale: A study of eight small, nested catchments in a temperate forested watershed

Current interest in multicatchment hydrologic studies challenges the use of geochemical mixing models across scale, where changes in stream water chemistry from catchment to catchment may indicate (1) changes in the proportional contributions of end‐members, (2) changes in the geochemical signatures of end‐members in space, or (3) changes in the geochemical signatures of end‐members in time. In this study we examine stream water chemistry from a series of eight nested catchments in a 1.47 km2 temperate forest watershed in southern Quebec for evidence of contributing end‐members. We use eigenvector and residual analysis (Hooper, 2003) of the multivariate stream water chemistry records to estimate the dimensionality of the mixing space for each individual catchment, indicating the number of contributing end‐members. Using the mixing space of the largest, highest‐order catchment (1.47 km2), we evaluate its ability to predict stream water chemistry in the seven upstream catchments, representing progressively smaller areas. We observe significant spatial variation in ionic mixing ratios within the 147 ha watershed. Only spatial testing across catchments allowed us to identify appropriate conservative tracers most compatible with the application of a single mixing model across scale. On the seasonal timescale, groundwater geochemistry changes significantly due to the recharge from spring snowmelt, indicating a mixture of two groundwater end‐members of varying age. On the timescale of storm events, shallow perched water and throughfall provide geochemical signatures consistent with physical mixing while unsaturated zone soil water sampled from local pockets of glacial till does not. Our results suggest cautious application of end‐member mixing analysis (EMMA) for multicatchment studies.

Changes in stream chemistry and nutrient export following a partial harvest in the Catskill Mountains, New York, USA

Clearcut forest harvesting typically results in large changes in stream water chemistry in northeastern North America. The effects of partial forest harvests on stream chemistry have not received as much attention, even though partial cutting is a more common forestry practice than clearcutting in this region. Changes in stream water chemistry following a partial cut are reported here from a 10 ha study catchment in a northern hardwood forest in the Catskill Mountains of southern New York, and are compared to those of a nearby 48 ha reference catchment. The lower two thirds of the treatment catchment was harvested in February–April 2002 by a shelterwood method, such that 33% of the basal area of the catchment was removed. Stream NO 3 −, NH 4 +, Ca 2+, K +, and total dissolved aluminum (Al to) concentrations increased significantly after the harvest. Stream Ca 2+, Mg 2+ and NH 4 + concentrations peaked 5 months after the initiation of the harvest, NO 3 − and K + concentrations peaked 6 months after cutting, and Al to concentrations peaked 1 year after cutting. Streamflow was not significantly affected by the harvest when compared to the flow of three nearby streams. Export of NO 3 − in stream water increased five-fold the year after the cut, and briefly exceeded atmospheric inputs of inorganic nitrogen during 4 months in the fall of 2002. Changes in stream NO 3 − and K + concentrations were less than predicted by the relative basal area removed compared with those of a recent nearby clearcut. In contrast, changes in Ca 2+, Mg 2+ and Al to concentrations were approximately proportional to basal area removal in these two cuts. Stream chemistry returned to values close to those of the pre-cut period and to reference values by early spring of 2003, just over a year after the initiation of the harvest, except for NO 3 − concentrations, which remained elevated above background 18–20 months after completion of the cut.

Simulating the long-term chemistry of an upland UK catchment: Major solutes and acidification

CHUM-AM was used to investigate changes in soil and water chemical variables in four moorland sub-catchments in Cumbria UK, to which non-marine S deposition has declined by 65% since the 1970s. The principal processes represented in the model comprise N and S uptake and release, water movements, the binding of cations by soil organic matter, chemical interactions in solution, and chemical weathering. CHUM-AM reproduced reasonably well the current soil pH and pools of N and S, and changes in streamwater chemistry over the period 1970–2000, notably decreases in the concentrations of alkaline earth cations and sulphate, and increases in pH. The model also predicts streamwater pH–Al relationships in agreement with observations. Predictive calculations suggest that constant atmospheric deposition of N at present rates will lead to N saturation and re-acidification, whereas a 50% reduction in N would stabilise soil and streamwater pH at about the present levels.

Modelling Changes in Stream Water Quality Due to Climate Change in a Southern Ontario Watershed

This research represents a pilot project to establish a methodology for assessing the sensitivity of watershed stream water quality to changes in water quantity caused by climate change. The pilot watershed is the Duffins Creek watershed, located 20 km east of the City of Toronto, Canada. Scenarios of climate change analyzed in this project were drawn from two internationally recognized climate models: the Canadian Centre for Climate Modelling and Analysis (CCCma) CGCM1 and the Hadley Centre HadCM2. The AGNPS (Agricultural Non-Point Source) model was used to predict changes in stream water chemistry. The results are compared to baseline conditions as well as future conditions based on 2020 land use scenarios. It was determined that 2020 land use scenarios typically result in much smaller changes in peak flows than are predicted for the climate change scenarios, especially the wet climate change scenarios. Understanding climate change responses is critical for the development of watershed plans and drinking water source protection studies. Currently, watershed studies are completed using climate information based on relatively short-term monitoring databases that reflect past weather patterns. It is widely understood that management actions advocated in watershed studies could be improved if consideration were given to the implication of climate changes.

Organic matter decomposition by fungi in a Mediterranean forested stream : contribution of streambed substrata

Aquatic microfungi play a fundamental role in organic matter decomposition in fluvial ecosystems. These micro-organisms degrade leaf recalcitrant compounds like lignin, thereby enhancing the utilization of organic material by the microbial community. The main input of allochthonous organic matter in Mediterranean streams occurs during the autumn. In-stream breakdown processes can be affected by high physical abrasion during flooding but changes in stream water chemistry may also affect decomposition enzymatic activities of stream microorganisms. We measured two ligninolytic activities (phenol oxidase and peroxidase) and a cellulolytic activity (cellobiohydrolase) in leaves, branches, sand and gravel substrata in a reach of a Mediterranean stream. Highest ligninolytic activities were measured in biofilm developed on inorganic substrata (sand and gravel) where also accumulated the highest fungal biomass (ranging from 3.3 x 10 -4 to 7.22 mg Ergosterol gAFDM -1 ) especially in sand substrata. Conversely, cellulolytic activities were significantly higher in biofilm on organic substrata (leaves and branches). Physical and chemical factors, such as discharge and stream water nutrient concentration (Dissolved Inorganic Nitrogen) were affecting enzymatic activities, particularly enhancing the phenol oxidase. Moreover, the chemical composition of the available OM (high cellulose in leaves, high lignin in detritic material) strongly influenced the decomposition activity in each biofilm. A precise description and quantification of the benthic substrata was used to obtain enzymatic activity values in terms of stream reach. Those results showed a temporal pattern in the decomposition activities in the reach, beginning with the decomposition of cellulose (October) followed by lignin compounds (November and December).

Calcium losses from a forested catchment in south-central Ontario, Canada.

Mass balance studies at a number of calibrated watersheds in eastern North America suggest that large losses of Ca from soil have occurred due to acid deposition. However, there is considerable controversy over whether losses have occurred from the exchangeable pool or whether there are other sources of Ca that have not been considered. Mass balance calculations at a small, calibrated catchment (PC1) in south-central Ontario also indicate that large losses of Ca have occurred over the past 2 decades. If the exchangeable Ca pool has declined by approximately 40% between 1983/1984 and 1998/1999 but the exchangeable Mg pool has remained relatively stable, these changes should be evident in streamwater chemistry. The slope of the buffer curve relating Ca to (sigma)acid anions (F(Ca)) decreased significantly over the study period. We estimate that F(Ca) decreased by 12-24% between 1983 and 1999, although the level of decrease is affected by changes in hydrology. During the same period, there was no significant change in F(Mg), and the annual volume-weighted Ca:Mg (equiv/equiv) ratio in streamwater decreased from approximately 2.8 to approximately 2.1. Measured changes in streamwater chemistry translate into Ca losses from the exchangeable pool of approximately 250-570 mequiv/m2 over the study period, which is similar to estimated losses based on soil measurements (approximately 425 mequiv/m2) and mass balance calculations (approximately 380-430 mequiv/m2). The magnitude of Ca loss cannot be explained by decreases in Ca deposition or decreased Ca weathering. Large Ca losses from the soil exchangeable pool have serious implications for future forest health and the recovery of streamwater from acid deposition.

Geochemical characteristics of runoff from acid sulfate soils in the northern area of Okinawa Island, Japan

The oxidation of pyrite in acid sulfate soils (ASS) produces high concentration of strong acid (H2SO4) in the soil. The acid reacts with soil minerals and dissolves aluminum and other acid-soluble metals. During rainfall, they are flushed and discharged into terrestrial and aquatic environments. The authors examined the chemical characteristics of the runoffs from ASS in Arashiyama and in Ooshitai, which are located in the northern part of Okinawa Island and evaluated their potential effects on surrounding environments. The results show that the runoffs were very acidic with pH range of 2.87 to 4.29, and minimum values were close to the pH values of the soils. The dominant species were SO42-, Al3+, and Fe2+ and they were well correlated with pH. The acidity of the runoffs caused dissolution of metals in the following order: Mn > Zn > Cu = Cd. The quality of runoffs was found to be poor and was mainly governed by the interaction of rain and soil. A comparison between the stream waters collected during rain event and on fine day showed a marked changes in stream water chemistry during rainfall as follows: alkalinity was reduced by 3.7 times, sulfate concentration was increased by 3 times whereas pH was decreased by 0.18 units. These changes are attributed to the contamination by runoff from ASS. Moreover brown flocky sediments were observed to have covered entire streambed at the discharging point. The chemical composition of the sediments shows that as those of runoffs, they were dominated by Fe, Al, and SO4. These results indicate that the sediments were mainly formed as the results of mixing runoffs and stream water.

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

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

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

Erratum: 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.

Long-term patterns of streamwater chemistry provide valuable evidence of the effects of environmental change on ecosystem biogeochemistry. Observations from old-growth forests may be particularly valuable, because patterns should not be influenced by forest succession. Water samples were collected biweekly from four streams in, and near, the old-growth forest watershed of the Bowl Research Natural Area in the White Mountains of New Hampshire from May 1973 through October 1974, and from June 1994 through June 1997. Average NO3– concentrations, which ranged from 40.8 to 46.1 µequiv.·L-1 in 1973-1974, declined significantly to averages of 14.9-20.1 µequiv.·L-1 during 1994-1997. Concentrations of the base cations, Ca2+ and Mg2+, also declined in stream water between the two sampling periods. The northeastern United States, including the study area, has been subjected to elevated atmospheric deposition of sulfur and nitrogen for more than 40 years. This observation has led to the concern that mature forest ecosystems may exhibit N saturation and depletion of Ca2+ from exchangeable soil pools. While the Bowl exhibits a pattern of elevated concentrations of NO3– throughout the year, suggestive of conditions of N saturation, concentrations have declined markedly over the last 20 years. Concentrations of Ca2+ have also declined suggesting possible depletion from the exchangeable soil pool, but the acid neutralizing capacity of stream water has remained constant or increased, indicating resistance to additional acidification.