Stream Water Nitrate Research Articles

Increase in stream water nitrate nitrogen concentrations caused by a disturbance to a forested catchment by Japanese oak wilt

ABSTRACTIn recent years, Japanese oak wilt (JOW) has become prevalent in Japan and has spread into almost all prefectures. To understand the effects of a JOW disturbance on nitrate nitrogen (NO3–) concentrations in a forest stream, we analyzed the changes in NO3– concentrations over a period of 7 years in a mixed broadleaved-conifer secondary forest in Japan. The JOW disturbance arose in the fifth year and lasted until the seventh year of the study period, resulting in a 4.7%, 3.0%, and 2.5% loss in the total basal area of the forest in the fifth, sixth, and seventh years, respectively, eventually resulting in an estimated canopy cover loss of 9.7%. The mean NO3– concentration after the appearance of JOW (3.99 μmol L–1) was significantly higher than before the start of the disturbance (1.99 μmol L–1). This study demonstrated that even the modest canopy cover loss by JOW-induced dieback of Quercus serrata trees could cause an increase in stream water NO3– concentration.

Recovery from acidification alters concentrations and fluxes of solutes from Czech catchments

Changes in atmospheric deposition, stream water chemistry, and solute fluxes were assessed across 15 small forested catchments. Dramatic changes in atmospheric deposition have occurred over the last three decades, including a 70% reduction in sulphur (S) deposition. These changes in atmospheric inputs have been associated with expected changes in levels of acidity, sulphate and base cations in streams. Soil retention of S appeared to partially explain rates of chemical recovery. In addition to these changes in acid–base chemistry we also observed unexpected changes in nitrogen (N) biogeochemistry and nutrient stoichiometry of stream water, including decreased stream N concentrations. Among all catchments the average flux of dissolved inorganic nitrogen (DIN) was best predicted by average runoff, soil chemistry (forest floor C/N) and levels of acid deposition (both S and N). The rate of change in stream DIN flux, however, was much more closely correlated with reductions in rates of S deposition rather than those of DIN. Unlike DIN fluxes, the average concentrations as well as the rates of decline in streamwater nitrate (NO3) concentration over time were tightly linked to stream dissolved organic carbon/dissolved organic nitrogen ratios DOC/DON and DON/TP rather than catchment characteristics. Declines in phosphorus adsorption with increasing soil pH appear to contribute to the relationship between C, N, and P in our study catchments. Our observations suggest that catchment P availability and its alteration due to environmental changes (e.g. acidification) might have profound effects on N cycling and catchment N retention that have been largely unrecognized.

Exploring impacts of vegetated buffer strips on nitrogen cycling using a spatially explicit hydro-biogeochemical modeling approach

Agriculture has been recognized as a major anthropogenic source of surplus loads of nitrogen in the environment. Losses of nitrate via subsurface pathways are severely threatening groundwater and surface waters. This study explored the capability of a coupled hydro-biogeochemical spatially explicit model, simulating nitrogen cycling in agricultural soils and the associated fate of excess nitrate subjected to vertical and lateral displacement towards water bodies. Different vegetated buffer strips (VBS) were tested for their nitrate retention capability and impacts on N2O and N2 emissions. The effectiveness of a VBS to remove nitrate by denitrification strongly depends on soil characteristics and hydrological flow paths. Simulated N2 emissions from VBS with high soil moisture were up to twenty-fold compared to VBS where groundwater levels were low. Simulated streamwater nitrate concentrations without VBS were 3.7 mg NO3− l−1 and showed a decrease to 0.1 mg NO3− l−1 for a 20 m VBS.

The response of tree ring δ15N to whole-watershed urea fertilization at the Fernow Experimental Forest, WV

Plant tissue δ15N is frequently used as a proxy for N availability and N cycle dynamics, and the δ15N signature of tree rings could potentially be used to reconstruct past changes in the N cycle due to forest disturbance or anthropogenic N deposition. However, there are substantial uncertainties regarding how effectively tree ring δ15N records N cycle dynamics. We used increment tree cores from a forested watershed that received a one-time application of urea, along with the long-term stream water chemistry record from that watershed and a nearby reference watershed, to determine the effectiveness of tree ring δ15N in recording a change in N availability, and whether its effectiveness differed by species or mycorrhizal type. Tree ring δ15N of three species increased rapidly (within ~1 to 3 years) following fertilization (Quercus rubra, Fagus grandifolia, and Prunus serotina), while that of Liriodendron tulipifera did not respond to fertilization but increased ~10 years later. Tree ring δ15N tended to remain elevated throughout the measured time period (1967–2000), well past the pulsed fertilization response in stream water. This extended δ15N response may be partially caused by chronic atmospheric N deposition in the region, which also contributed to greater losses of nitrate in stream water by ~1980. Additionally, local recycling of N compounds, and retranslocation of N within the trees, may account for the persistence of elevated tree ring δ15N levels beyond the direct fertilization effects. Collectively, these results confirm that tree ring δ15N from some species can document the onset of historical changes in the N cycle. We suggest that studies utilizing tree ring δ15N as a proxy for long-term N cycle dynamics should look for a consistent pattern of change among several species rather than relying on the record from a single species.

A Decade of Streamwater Nitrogen and Forest Dynamics after a Mountain Pine Beetle Outbreak at the Fraser Experimental Forest, Colorado

Forests of western North America are currently experiencing extensive tree mortality from a variety of bark beetle species, and insect outbreaks are projected to increase under warmer, drier climates. Unlike the abrupt biogeochemical changes typical after wildfire and timber harvesting, the outcomes of insect outbreaks are poorly understood. The mountain pine bark beetle (Dendroctonus ponderosae) began to attack lodgepole pine (Pinus contorta) at the Fraser Experimental Forest in 2002 and spread throughout the research area by 2007. We compared streamwater nitrogen (N) from 2003 through 2012 with data from the previous two decades in four watersheds with distinct forest management histories, stand structures, and responses to the beetle outbreak. Watersheds dominated by old-growth had larger trees and lost 85% of overstory pine and 44% of total basal area to bark beetles. In contrast, managed watersheds containing a mixture of second-growth (30–60 year old) and old-growth (250- to 350-year old) had higher density of subcanopy trees, smaller mean tree diameter, and lower bark beetle-induced mortality (~26% of total basal area). Streamwater nitrate concentrations were significantly higher in old-growth watersheds during the outbreak than pre-outbreak levels during snowmelt and base flow seasons. In mixed-age stands, streamwater nitrate concentrations were unaffected by the outbreak. Beetle outbreak elevated inorganic N export 43 and 74% in two old-growth watersheds though the amounts of N released in streamwater were low (0.04 and 0.15 kg N ha−1) relative to atmospheric inputs (<2% of annual N deposition). Increased height, diameter, and foliar N of measured in residual live trees augmented demand for N, far in excess of the change in N export during the outbreak. Reallocation of soil resources released after pine mortality to overstory and understory vegetation helps explain high nutrient retention in watersheds affected by bark beetle outbreaks.

Spatial and temporal variations in nitrogen export from a New Zealand pastoral catchment revealed by stream water nitrate isotopic composition

AbstractViable indicators of nitrogen (N) attenuation at the catchment scale are needed in order to sustainably manage global agricultural intensification. We hypothesized that the dominance of a single land use (pasture production) and strong ground‐to‐surface water connectivity would combine to create a system in which surface water nitrate isotopes (δ15N and δ18O of ) could be used to monitor variations in catchment‐scale attenuation. Nitrate isotopes were measured monthly over a 2 year period in four reaches along a spring‐fed, gaining stream (mean ‐N of 6 mg L−1) in Canterbury, New Zealand. The stream water pool indicated that the highest degree of denitrification occurred in the shallow upper reaches. Moving downstream through increasingly sandy soils, the isotopic signature of denitrification became progressively weaker. The lowest reaches fell into the expected range for produced from the nitrification of pasture N sources (urine and fertilizers), implying that the attenuation capacity of the groundwater and riparian systems was lower than the rate of N inputs. After excluding months affected by effluent spills or extreme weather (n = 4), variations in the degree of denitrification over stream distance were combined with the measured discharge to estimate N attenuation over time in the subcatchment. Attenuation was highly responsive to rainfall: 93% of calculated attenuation (20 kg ‐N ha−1 yr−1) occurred within 48 h of rainfall. These findings demonstrate the potential for detailed stable isotope data to provide integrative measures of catchment loss pathways.

Dual nitrate isotopes clarify the role of biological processing and hydrologic flow paths on nitrogen cycling in subtropical low‐gradient watersheds

AbstractNitrogen (N) is an important nutrient as it often limits productivity but in excess can impair water quality. Most studies on watershed N cycling have occurred in upland forested catchments where snowmelt dominates N export; fewer studies have focused on low‐relief watersheds that lack snow. We examined watershed N cycling in three adjacent, low‐relief watersheds in the Upper Coastal Plain of the southeastern United States to better understand the role of hydrological flow paths and biological transformations of N at the watershed scale. Groundwater was the dominant source of nitrified N to stream water in two of the three watersheds, while atmospheric deposition comprised 28% of stream water nitrate in one watershed. The greater atmospheric contribution may have been due to the larger stream channel area relative to total watershed area or the dominance of shallow subsurface flow paths contributing to stream flow in this watershed. There was a positive relationship between temperature and stream water ammonium concentrations and a negative relationship between temperature and stream water nitrate concentrations in each watershed suggesting that N cycling processes (i.e., nitrification and denitrification) varied seasonally. However, there were no clear patterns in the importance of denitrification in different water pools possibly because a variety of factors (i.e., assimilatory uptake, dissimilatory uptake, and mixing) affected nitrate concentrations. Together, these results highlight the hydrological and biological controls on N cycling in low‐gradient watersheds and variability in N delivery flow paths among adjacent watersheds with similar physical characteristics.

Recovery from chronic and snowmelt acidification: Long‐term trends in stream and soil water chemistry at the Hubbard Brook Experimental Forest, New Hampshire, USA

AbstractAtmospheric acid deposition of sulfate and nitrate has declined markedly in the northeastern United States due to emissions controls. We investigated long‐term trends in soil water (1984–2011) and stream water (1982–2011) chemistry along an elevation gradient of a forested watershed to evaluate the progress of recovery of drainage waters from acidic deposition at the Hubbard Brook Experimental Forest in the White Mountains of New Hampshire, USA. We found slowed losses of base cations from soil and decreased mobilization of dissolved inorganic aluminum. Stream water pH at the watershed outlet increased at a rate of 0.01 units yr−1, and the acid neutralizing capacity (ANC) gained 0.88 µeq L−1 yr−1. Dissolved organic carbon generally decreased in stream water and soil solutions, contrary to trends observed at many North American and European sites. We compared whole‐year hydrochemical trends with those during snowmelt, which is the highest‐flow and lowest ANC period of the year, indicative of episodic acidification. Stream water during snowmelt had long‐term trends of increasing ANC and pH at a rate very similar to the whole‐year record, with closely related steady decreases in sulfate. A more rapid decline in stream water nitrate during snowmelt compared with the whole‐year trend may be due, in part, to the marked decrease in atmospheric nitrate deposition during the last decade. The similarity between the whole‐year trends and those of the snowmelt period is an important finding that demonstrates a consistency between recovery from chronic acidification during base flow and abatement of snowmelt acidification.

Mechanisms driving the seasonality of catchment scale nitrate export: Evidence for riparian ecohydrologic controls

AbstractConsiderable variability in the seasonal patterns of stream water nitrate ( ) has been observed in forested watersheds throughout the world. While many forested headwater catchments exhibit winter and early spring peaks in concentrations, several watersheds have peak concentrations during the summer months. Pond Branch, a headwater catchment in Maryland monitored for over 10 years, exhibits recurrent and broad summer peaks in both concentrations and watershed export. Higher export from June to September is particularly surprising, given that these summer months typically have the year's lowest discharge. A key challenge is identifying the source(s) of and the mechanism(s) by which it is transported to the watershed outlet during the summer. In this study, we assessed multiple hypotheses (not mutually exclusive) that could account for the seasonal trend including proximal controls of groundwater‐surface water interactions, instream processes, and riparian groundwater‐N cycling interactions, as well as two distal controls: geochemical weathering and senescence of riparian vegetation. A combination of long‐term weekly and limited duration high‐frequency sensor data reveals the importance of riparian ecohydrologic processes during base flow. In this watershed, patterns of seasonal stream water concentrations and fluxes depend fundamentally on interactions between groundwater dynamics and nitrogen (N) cycling in the riparian zone. Groundwater tables control nitrification‐denitrification dynamics as well as hydrologic transport. Our results suggest that in many watersheds, a more sophisticated exploration of production and transport mechanisms is required to identify critical points in the landscape and over time that disproportionately drive patterns of watershed export.

Organic forms dominate hydrologic nitrogen export from a lowland tropical watershed.

Observations of high dissolved inorganic nitrogen (DIN) concentrations in stream water have reinforced the notion that primary tropical rain forests cycle nitrogen (N) in relative excess compared to phosphorus. Here we test this notion by evaluating hydrologic N export from a small watershed on the Osa Peninsula, Costa Rica, where prior research has shown multiple indicators of conservative N cycling throughout the ecosystem. We repeatedly measured a host of factors known to influence N export for one year, including stream water chemistry and upslope litterfall, soil N availability and net N processing rates, and soil solution chemistry at the surface, 15- and 50-cm depths. Contrary to prevailing assumptions about the lowland N cycle, we find that dissolved organic nitrogen (DON) averaged 85% of dissolved N export for 48 of 52 consecutive weeks. For most of the year stream water nitrate (NO3-) export was very low, which reflected minimal net N processing and DIN leaching from upslope soils. Yet, for one month in the dry season, NO3- was the major component of N export due to a combination of low flows and upslope nitrification that concentrated NO3- in stream water. Particulate organic N (PON) export was much larger than dissolved forms at 14.6 kg N x ha(-1) x yr(-1), driven by soil erosion during storms. At this rate, PON export was slightly greater than estimated inputs from free-living N fixation and atmospheric N deposition, which suggests that erosion-driven PON export could constrain ecosystem level N stocks over longer timescales. This phenomenon is complimentary to the "DON leak" hypothesis, which postulates that the long-term accumulation of ecosystem N in unpolluted ecosystems is constrained by the export of organic N independently of biological N demand. Using an established global sediment generation model, we illustrate that PON erosion may be an important vector for N loss in tropical landscapes that are geomorphically active. This study supports an emerging view that landscape geomorphology influences nutrient biogeochemistry and limitation, though more research is needed to understand the mechanisms and spatial significance of erosional N loss from terrestrial ecosystems.

Comparing the influence of wildfire and prescribed burns on watershed nitrogen biogeochemistry using 15N natural abundance in terrestrial and aquatic ecosystem components.

We evaluated differences in the effects of three low-severity spring prescribed burns and four wildfires on nitrogen (N) biogeochemistry in Rocky Mountain headwater watersheds. We compared paired (burned/unburned) watersheds of four wildfires and three spring prescribed burns for three growing seasons post-fire. To better understand fire effects on the entire watershed ecosystem, we measured N concentrations and δ15N in both the terrestrial and aquatic ecosystems components, i.e., soil, understory plants in upland and riparian areas, streamwater, and in-stream moss. In addition, we measured nitrate reductase activity in foliage of Spiraea betulifolia, a dominant understory species. We found increases of δ15N and N concentrations in both terrestrial and aquatic ecosystem N pools after wildfire, but responses were limited to terrestrial N pools after prescribed burns indicating that N transfer from terrestrial to aquatic ecosystem components did not occur in low-severity prescribed burns. Foliar δ15N differed between wildfire and prescribed burn sites; the δ15N of foliage of upland plants was enriched by 2.9 ‰ (difference between burned and unburned watersheds) in the first two years after wildfire, but only 1.3 ‰ after prescribed burns. In-stream moss δ15N in wildfire-burned watersheds was enriched by 1.3 ‰, but there was no response by moss in prescription-burned watersheds, mirroring patterns of streamwater nitrate concentrations. S. betulifolia showed significantly higher nitrate reductase activity two years after wildfires relative to corresponding unburned watersheds, but no such difference was found after prescribed burns. These responses are consistent with less altered N biogeochemistry after prescribed burns relative to wildfire. We concluded that δ15N values in terrestrial and aquatic plants and streamwater nitrate concentrations after fire can be useful indicators of the magnitude and duration of fire effects and the fate of post-fire available N.

Regional nitrogen dynamics in the TERENO Bode River catchment, Germany, as constrained by stable isotope patterns

Interactions between hydrological characteristics and microbial activities affect the isotopic composition of dissolved nitrate in surface water. Nitrogen and oxygen isotopic signatures of riverine nitrate in 133 sampling locations distributed over the Bode River catchment in the Harz Mountains, Germany, were used to identify nitrate sources and transformation processes. An annual monitoring programme consisting of seasonal sampling campaigns in spring, summer and autumn was conducted. δ15N and δ18O of nitrate and corresponding concentrations were measured as well as δ2H and δ18O of water to determine the deuterium excess. In addition, precipitation on 25 sampling stations was sampled and considered as a potential input factor. The Bode River catchment is strongly influenced by agricultural land use which is about 70 % of the overall size of the catchment. Different nitrogen sources such as ammonia (NH4) fertilizer, soil nitrogen, organic fertilizer or nitrate in precipitation show partly clear nitrate isotopic differences. Processes such as microbial denitrification result in fractionation and lead to an increase in δ15N of nitrate. We observed an evident regional and partly temporal variation of nitrate isotope signatures which are clearly different between main landscape types. Spring water sections within the high mountains contain nitrate in low concentrations with low δ15NNO3 values of −3 ‰ and high δ18ONO3 values up to 13 ‰. High mountain stream water sub-catchments dominated by nearly undisturbed forest and grassland contribute nitrate with δ15NNO3 and δ18ONO3 values of −1 and −3.5 ‰, respectively. In the further flow path, which is affected by an increasing agricultural land use and urban sewage, we recognized an increase in δ15NNO3 and δ18ONO3 up to 22 and 18 ‰, respectively, with high variations during the year. A correlation seems to exist between the percentage of agricultural land use area and the corresponding δ15NNO3 values for sub-catchments. A shift towards heavier isotope values in stream water samples taken in July 2012 is significant (p-value = 6 · 10−6) compared to samples from March and October 2012. We also see a season-depending impact of microbial denitrification. Denitrification, especially evident in the lowlands, predominantly takes place in the riverbeds. In addition, mixing processes of different nitrate sources and temperature-depending biological processes such as nitrification have to be taken into consideration. Constant-tempered groundwater does not play a noticeable role in the processes of the stream water system. As constrained from oxygen isotope signatures, precipitation associated with low nitrate concentrations does not have an obvious impact on stream water nitrate in the high mountain region.

Quantification of Nitrate Sources to an Urban Stream Using Dual Nitrate Isotopes

Human-engineered landscapes and subsequent altered hydrology affect the fate and transport of reactive nitrogen, particularly in urban watersheds. In this study, we used dual-nitrate isotopes and mixing model analysis (δ(15)N and δ(18)O of NO3(-)) to quantify nitrogen inputs from two sources concentrated in urban systems, sewage and atmospheric deposition. Analysis was conducted on samples collected from Nine Mile Run (Pittsburgh, PA) including over two years of samples collected biweekly and samples collected through the hydrographs of four storm events. Mixing models incorporated uncertainties in the isotopic composition of potential nitrate sources and resolved the relative proportions of nitrate inputs from each source using Bayesian techniques. The results indicate that up to 94% of nitrate in streamwater originated from sewage sources during baseflow conditions. During storms, atmospheric deposition was a substantial nitrate source (∼ 34%) to total event-based nitrate loads, although sewage-derived nitrate remained the dominant source (66%). The potential influence of denitrification was considered by incorporating associated isotopic fractionations into mixing models; up to 19% of sewage-derived samples showed the isotopic effects of denitrification. This study quantitatively delineates proportions of nitrate from different sources to urban streamwater, while incorporating remaining uncertainties in source endmember compositions.

Linking soils and streams: Response of soil solution chemistry to simulated hurricane disturbance mirrors stream chemistry following a severe hurricane

Understanding the drivers of forest ecosystem response to major disturbance events is an important topic in forest ecology and ecosystem management. Because of the multiple elements included in most major disturbances such as hurricanes, fires, or landslides, it is often difficult to ascribe a specific driver to the observed response. This is particularly true for the long-term effects of hurricanes on forest ecosystem nutrient cycling. Hurricane disturbance opens the forest canopy by removing leaves and branches or snapping boles, and in so doing turns living biomass into debris that is deposited on the forest floor. At the watershed scale, past work in the Luquillo Mountains of Puerto Rico shows that these changes in forest structure and detrital dynamics result in large increases in stream water nitrate and potassium concentrations in streams draining volcaniclastic terrain. The Canopy Trimming Experiment (CTE) was designed to simulate the major effects of hurricane disturbance, and disentangle the effects of canopy opening and debris addition on forest biology and biogeochemistry following a hurricane. Using the chemistry of soil solution as an integrated indicator of biogeochemical response to hurricane simulation, the experimental manipulations show that the synergistic effects of both canopy opening and debris addition are needed to elicit one of the whole-watershed responses to hurricanes, a large pulse of nitrate (NO3) concentration in stream water that lasted approximately 18months. Manipulation of either canopy openness or debris addition alone had little effect on soil solution chemistry for NO3, or for any other solute measured (dissolved organic matter, phosphate, ammonium, major cations and anions, and silica). None of the treatments resulted in the increased potassium (K) seen in stream water following hurricane disturbance. For NO3, the time course of response and recovery following combined treatments of canopy opening and debris addition was similar to that observed in stream water after actual hurricanes. The CTE provided further evidence that tree regrowth following hurricane disturbance controls the return of NO3 concentrations to pre-hurricane levels in this tropical forest. The lack of response in K to hurricane simulation suggests that leaching of the added debris, which was not captured in the experimental manipulations, is a major driver of K concentrations following disturbance. Hurricane disturbance, which is significant in many humid tropical forests, results in pulsed outputs of nitrogen in stream water that can be clearly ascribed to interactions between damage and recovery of canopy vegetation, and decomposition of detrital inputs on the forest floor.

Chemical flushing from an urban-fringe watershed: hydrologic and riparian soil dynamics

The goal of the current study is to better understand the role of storm dynamics on stream water chemical variability in a highly polluted urban-fringe watershed. The study was conducted in the upper reach of the Arroyo Seco watershed located on the eastern edge of the densely urbanized Los Angeles basin in California. During the 2008–2009 study period, high-frequency stream water observations of chloride, fluoride, sulfate, and nitrate were monitored through a series of storm events and were compared to pre- and post-winter storm season geochemical soil profiles. Of the four solutes measured, nitrate demonstrated hydrologically enhanced behavior. Chloride, fluoride, and sulfate exhibited enhanced behavior initially (first flush), but transitioned to dilution behavior as the season progressed. Soil chemistry analyses in the riparian zone confirmed the abundance of nitrate on the soil surface, serving as a source for stream water nitrate. Observations and analyses collectively suggest that the chemical variability observed during the storms is dependent not only on discharge, but also on the magnitude and intensity of rainfall, the length of the antecedent dry period, and riparian soil composition. A further understanding of these factors will ultimately improve geochemical models for prediction of downstream chemical loads from regional urban-fringe watersheds.

Hydrologic Connectivity in the High-Elevation Tropics: Heterogeneous Responses to Land Change

In the high-elevation humid tropics, human- and climate-driven land transitions can alter hydrologic connections between the atmosphere and surface waters, with local and downstream effects. We conducted a data synthesis to examine the influence of forest-to-grassland conversion, agroforest-to-nonforest conversion, tree plantation establishment on nonforest land, and recent glacier retreat on throughfall, evapotranspiration, runoff, and nitrate fluxes in montane Latin America (including the Caribbean) and Hawaii. Our synthesis reveals heterogeneous—sometimes unexpected—responses to land change. For example, in contrast with temperate highlands, forest-to-grassland conversion in the high-elevation tropics often results in little runoff increase and lower streamwater nitrate loss. Tree plantation establishment leads to diminished runoff; the magnitude of this effect is tenfold greater than with forest-to-grassland transitions. We highlight cases in which land use, land cover, and water relationships derived from temperate ecosystems do not apply to and, therefore, should not underpin watershed management programs in the high-elevation tropics.

Calcium concentration in leaf litter affects the abundance and survival of crustaceans in streams draining warm–temperate forests

Summary Stream ecosystems receive large quantities of nutrients from terrestrial ecosystems that influence community dynamics. However, few studies have investigated the effects of subsidiary calcium, an essential element of animals, on stream ecosystems. We focused on differences in calcium concentrations of leaf litter between tree species. In particular, litter of Japanese cedar (Cryptomeria japonica) has a higher concentration of calcium than other taxa, and the tree is planted in many parts of Japan. Therefore, we predicted that a C. japonica plantation would affect the supply of subsidiary calcium to stream ecosystems. We compared calcium concentration of leaf litters, soils, stream water and stream benthic invertebrates sampled at nine sites in catchments composed of cedar plantations, evergreen broad‐leaved forest and clear‐cut areas. In addition, we placed 10 Gammarus nipponensis in each of 10 nylon cages in the nine streams and after one month surveyed the number of surviving individuals. Calcium concentration in stream water and soil, and the density and survival of the dominant crustacean (Gammarus nipponensis) were significantly higher at sites dominated by C. japonica compared with other forest types. Furthermore, invertebrate community composition was correlated with total calcium and nitrate in stream water, indicating that terrestrial vegetation can affect stream invertebrate communities, particularly crustaceans.

Upland streamwater nitrate dynamics across decadal to sub-daily timescales: a case study of Plynlimon, Wales

Abstract. Streamwater nitrate dynamics in the River Hafren, Plynlimon, mid-Wales were investigated over decadal to sub-daily timescales using a range of statistical techniques. Long-term data were derived from weekly grab samples (1984–2010) and high-frequency data from 7-hourly samples (2007–2009) both measured at two sites: a headwater stream draining moorland and a downstream site below plantation forest. This study is one of the first to analyse upland streamwater nitrate dynamics across such a wide range of timescales and report on the principal mechanisms identified. The data analysis provided no clear evidence that the long-term decline in streamwater nitrate concentrations was related to a decline in atmospheric deposition alone, because nitrogen deposition first increased and then decreased during the study period. Increased streamwater temperature and denitrification may also have contributed to the decline in stream nitrate concentrations, the former through increased N uptake rates and the latter resultant from increased dissolved organic carbon concentrations. Strong seasonal cycles, with concentration minimums in the summer, were driven by seasonal flow minimums and seasonal biological activity enhancing nitrate uptake. Complex diurnal dynamics were observed, with seasonal changes in phase and amplitude of the cycling, and the diurnal dynamics were variable along the river. At the moorland site, a regular daily cycle, with minimum concentrations in the early afternoon, corresponding with peak air temperatures, indicated the importance of instream biological processing. At the downstream site, the diurnal dynamics were a composite signal, resultant from advection, dispersion and nitrate processing in the soils of the lower catchment. The diurnal streamwater nitrate dynamics were also affected by drought conditions. Enhanced diurnal cycling in Spring 2007 was attributed to increased nitrate availability in the post-drought period as well as low flow rates and high temperatures over this period. The combination of high-frequency short-term measurements and long-term monitoring provides a powerful tool for increasing understanding of the controls of element fluxes and concentrations in surface waters.

Nitrate reductase activity in chosen mosses: a case of study in skalny colliery waste tip / Aktywność reduktazy azotanowej u wybranych mchów na przykładzie hałdy powęglowej skalny

Abstract Two species of mosses in relation to nitrogen metabolism were examined. This subject is little known in this group of plant. Investigations of nitrate reductase activity in green tissues of Brachythecium rutabulum (Hedw.) Schimp. and Atrichum undulatum (Hedw.) P.Beauv. were performed. The study was conducted in two localities: heavy contaminated waste tip Skalny located in Upper Silesia, and Blonia City Park in Bielsko-Biala which place was chosen as a control area. For both species high activity of the enzyme was detected. The nitrate reductase activity varied between 99 to 9093 nmol per g dry mass per hour for B. rutabulum and 265 to 5135 nmol per g d.m. per hour of nitrite synthesized for A. undulatum respectively on Skalny waste tip. In the control area the results varied between 747 to 1077 for B. rutabulum and 171 to 518 nmol per g d.m. per hour of nitrite synthesized for A. undulatum, respectively. The differences were statistically significant only between the two species but not between habitats probably due to high dispersion and small amount of replications. The levels of nitrate and nitrite in stream water in both areas were also measured. In the Skalny waste tip there were high and reached 1.66 mg · dm-3 of nitrite and 65 mg · dm-3 of nitrate, respectively. In the control area these amounts were lower and reach zero level for nitrite and 4.5 mg · dm-3 of nitrate, respectively.

Contrasts among macrophyte riparian species in their use of stream water nitrate and ammonium: insights from 15N natural abundance

We examined the relevance of dissolved inorganic nitrogen (DIN) forms (nitrate and ammonium) in stream water as N sources for different macrophyte species. To do this, we investigated the variability and relationships between 15N natural abundance of DIN forms and of four different macrophyte species in five different streams influenced by inputs from wastewater treatment plants and over time within one of these streams. Results showed that 15N signatures were similar in species of submersed and amphibious macrophytes and in stream water DIN, whereas 15N signatures of the riparian species were not. 15N signatures of macrophytes were generally closer to 15N signatures of nitrate, regardless of the species considered. Our results showed significant relationships between 15N signatures of DIN and those of submersed Callitriche stagnalis and amphibious Veronica beccabunga and Apium nodiflorum, suggesting stream water DIN as a relevant N source for these two functional groups. Moreover, results from a mixing model suggested that stream water DIN taken up by the submersed and amphibious species was mostly in the form of nitrate. Together, these results suggest different contribution to in-stream N uptake among the spatially-segregated species of macrophytes. While submersed and amphibious species can contribute to in-stream N uptake by assimilation of DIN, macrophyte species located at stream channel edges do not seem to rely on stream water DIN as an N source. Ultimately, these results add a functional dimension to the current use of macrophytes for the restoration of stream channel morphology, indicating that they can also contribute to reduce excess DIN in streams.