Stream Load Research Articles

Linking Dominant Rainfall‐Runoff Event Hydrologic Response Dynamics With Nitrate and Chloride Load Estimates of Three Boreal Shield Catchments

AbstractUnderstanding hydrological dynamics in boreal Shield catchments is critical for projecting changes in stream runoff and chemistry in a region that is, sensitive to climate change. Previous work has mostly focused on a limited number of events over one or a few seasons because of the relative scarcity of high‐frequency datasets and automated tools for rainfall‐runoff event delineation. For the boreal region, a greater understanding of seasonality in hydrologic response and solute export related to rainfall‐initiated events is needed, as significant shifts in hydrologic regimes from climate change are expected. This study aimed to help resolve these knowledge gaps by assessing event‐scale hydrologic response dynamics and stream loads of nitrate and chloride using long‐term data from three boreal Shield catchments. Hydrometric and stream chemistry data from 2001 to 2018 were analyzed to delineate rainfall‐runoff events and estimate event nitrate and chloride loads. Event hydrologic response and loads were highly variable, especially with respect to catchment runoff initiation. Only subtle differences in hydrologic response dynamics were observed between summer and fall events, while seasonal differences in event nitrate and chloride loads were most statistically significant. Interestingly, a wide range of rainfall‐runoff events classified by response magnitude and timing was associated with differences in nitrate and chloride export. This study further confirms the utility of long‐term high‐frequency datasets and illustrates the need for additional work to further assess long‐term changes in event‐based hydrologic response and stream solute concentrations in the boreal region.

Critical loads of headwater streams in China using SSWC model modified by comprehensive F-factor

In order to evaluate the potential risk of surface water acidification in regions with historically-elevated acid deposition and to measure the recovery of such ecosystems after policy changes, critical loads and their exceedances were estimated for 349 headwater streams across China using a modified SSWC model. Such a model considered the acid-neutralizing capacity derived from high base cation deposition and the robust retention of sulfate and nitrate. Results indicated that China's streams had higher critical loads (averaged at 4.7 keq·ha−1·yr−1) and were less sensitive to acid deposition as compared to Europe and North America. The proportion of surveyed streams with acid deposition exceeded critical load decreased from 40.4% in 2005 to 29.5% in 2018, indicating a significant decrease in risk of surface water acidification, and thus a benefit from the emission abatement in recent years. Nonetheless, a relatively high risk of acidification still existed in southeast China with lower critical loads and most critical load exceedances. More efforts should be put into implementing emission control policies in the future.

Estimating simazine-treated area in watersheds based on annual stream loads.

Existing data in the United States are insufficient for estimating pesticide-treated crop areas at the watershed scale. The objective of this research was to evaluate an approach for estimating simazine usage on corn (Zea mays L.) based on its transport to streams of the Salt River Basin (SRB) of Missouri, USA. Annual loads of total simazine and atrazine (parent + metabolites) were quantified for seven SRB watersheds from 2005 to 2017. Simazine-treated corn area was computed as the total simazine load (g) divided by total atrazine load (g ha-1 ) on a treated area basis; atrazine was used as surrogate in the absence of treated area simazine load data. From 2005 to 2010, an estimated 3.8-31% of the corn area within SRB watersheds was treated with simazine, and four of six watersheds had<10% of corn treated. In contrast, Long Branch Creek (2005-2017) and its sub-watersheds (2012-2017) had≥20% of corn area treated with simazine. Key sources of variation in treated area estimates included extremely dry years with little simazine transport and disparities between spring-applied atrazine and fall-applied simazine transport. However, compared with national estimates for the SRB, these results estimated simazine usage that was generally one to two orders of magnitude greater and showed far more spatial and temporal variation among watersheds. These results demonstrated that this broadly applicable output-based method is a significant improvement over existing input-based national data for estimating pesticide usage in watersheds.

The impact of stream‐groundwater exchange on seasonal nitrate loads in an urban stream

AbstractUrbanization negatively impacts water quality in streams by reducing stream‐groundwater interactions, which can reduce a stream's capacity to naturally attenuate nitrate. Meadowbrook Creek, a first order urban stream in Syracuse, New York, has an inverse urbanization gradient, with heavily urbanized headwaters that are disconnected from the floodplain and downstream reaches that have intact riparian floodplains and connection to riparian aquifers. This system allows assessment of how stream‐groundwater interactions in urban streams impact the net sources and sinks of nitrate at the reach scale. We used continuous (15‐min) streamflow measurements and weekly grab samples at three gauging stations positioned longitudinally along the creek to develop continuous nitrate load estimates at the inlet and outlet of two contrasting reaches. Nitrate load estimates were determined using a USGS linear regression model, RLOADEST, and differences between loads at the inlet and outlet of contrasting reaches were used to quantify nitrate sink and source behaviour year‐round. We observed a nitrate load of 1.4 × 104 kg NO3− per water year, on average, at the outlet of the urbanized reach while the nitrate load at the outlet of the downstream, connected reach was 1.0 × 104 kg NO3− per water year, on average. We found the more heavily urbanized, hydrologically‐disconnected reach was a net source of nitrate regardless of season. In contrast, stream‐groundwater exchange caused the hydrologically connected reach to be both a source and sink for nitrate, depending on time of year. Both reaches alter nitrate source and sink behaviour at various spatiotemporal scales. Groundwater connection in the downstream, connected reach reduces annual nitrate loads and provides more opportunities for sources and sinks of nitrate year‐round than the hydrologically disconnected stream reach. Mechanisms include groundwater discharge into the stream with variable nitrate concentrations, surface‐water groundwater interactions that foster denitrification, and stream load loss to surrounding near‐stream aquifers. This study emphasizes how loads are important in understanding how stream‐groundwater interactions impact reach scale nitrate export in urban streams.

A flow-weighted approach to generate daily total phosphorus loads in streams based on seasonal loads

Phosphorus (P) is an essential nutrient for all forms of life but its over-enrichment can result in eutrophication of surface waters. For many watersheds around the world, some seasonal total P (TP) load datasets may exist but the continuous and multi-year daily TP concentrations and/or load datasets are not available due to the lacks of in situ P sensor measurement, time-consuming, and budget constraint. Traditionally, the seasonal TP loads are normally obtained with measuring daily TP concentrations for a couple of times within a season in a watershed, and then these daily TP concentrations along with their respective daily discharges are used to calculate the seasonal TP loads for the watershed. However, without the continuous and multi-year daily TP load dataset, development of total maximum daily load (TMDL) and calibration of watershed models for TP cannot be achieved. A flow-weighted method was developed (with detailed procedures) here to generate the daily TP loads based on the seasonal loads. The method was rigorously validated using the measured daily TP datasets from three different US Geological Survey gage stations. With very good statistical comparisons between the method predicted and field measured TP loads, we demonstrated that the flow-weighted method herein is a useful tool to disaggregate the seasonal TP loads into the daily TP loads when the measured daily TP data are not available while the TMDL development and model calibrations/validations are inevitable.

Baseline Study on Microplastics in Indian Rivers under Different Anthropogenic Influences

Microplastic particles are found in environmental compartments all over the world and receive a great deal of attention, especially in the aquatic environment. Currently, a particularly high input of microplastics via Asian rivers is assumed, but so far, there are hardly any data through field measurements. Three rivers in South India were considered for this purpose to focus on their microplastic load. The emphasis was on the comparison of microplastic concentrations in urban and rural rivers. While two rivers in the megacity Chennai (Tamil Nadu) were found to have an average microplastic concentration of 0.4 microplastic particles/L, a rural river near Munnar (Kerala) had an average concentration of 0.2 microplastic particles/L. Rough estimates of annual microplastic discharge from the Adyar River (Chennai) into the Bay of Bengal are found to be as high as 11.6 trillion microplastic particles. This study should be one of the first baseline studies for microplastic loads in South Indian streams and should be complemented with further environmental sampling before, during and after the monsoon season to get more detailed information on the storage and transportation of fluvial microplastics under different weather conditions.

Three decades of regulation of agricultural nitrogen losses: Experiences from the Danish Agricultural Monitoring Program

Excess nitrogen (N) losses from intensive agricultural production are a world-wide problem causing eutrophication in vulnerable aquatic ecosystems such as estuaries. Therefore, Denmark as one of the most intensively farmed countries in the world has enforced mandatory regulations on agricultural production since the late 1980s. We demonstrate the outcome of the regulations imposed on agriculture by analyzing decadal trends in nitrate (NO3−) concentrations and loads in streams using 29 years of detailed monitoring data and survey information on agricultural practices at field level from five intensively cultivated headwater catchments. The analysis includes the importance of four main drivers (climate, land use, agricultural practices, and biogeophysical properties of catchments), each divided into different factors that may influence stream NO3− loads during three subperiods defined by the time of introduction of different mitigation measures: i) 1990–1998, ii) 1999–2007, and iii) 2008–2018.Significant correlations with annual flow-weighted stream NO3− concentrations and/or loads were found for factors representing all of the four main drivers including precipitation, large scale climate fluctuations, runoff, previous year's runoff, baseflow index, number of annual frost days, agricultural area, livestock density, field N surplus, catch crop cover, manure storage capacity, method and time of manure spreading, and time of soil tillage.Changes in the four drivers were reflected by the load-runoff (L-Q) relationships for each of the three subperiods within each of the five headwater catchments. The five catchments experienced large but catchment-specific downward shifts in the L-Q relationship attributable to changes in land use and agricultural management within the catchments. The documented large downward shifts in NO3− loads demonstrated for the five catchments (30–52%) as a consequence of mandatory regulation over a period of nearly three decades are a unique example of how agriculture can reduce its environmental impact.

Spatial variability in water quality and macroinvertebrate assemblages across a disturbance gradient in the Mara River Basin, Kenya

Across the Afrotropical ecosystems human activities are increasingly modifying natural flow regimes, nutrient and organic matter loading and processing in streams and rivers with implications on ecosystem structure and functioning. The Mara River Basin has undergone extensive land-use change, but influences of these changes on water quality and aquatic communities are not well understood. This study investigated changes in water quality and macroinvertebrate assemblages across a disturbance gradient arising from rural human activities in nineteen sites; grouped into three condition categories (reference undisturbed (n = 7), moderately disturbed (n = 6) and disturbed (n = 6)). Temperature, dissolved oxygen, total dissolved solids, pH and electrical conductivity were measured in situ at each sampling site, and samples collected for analysis of nutrients and total suspended solids. Sampled macroinvertebrates were identified mainly to family level for analysis of structural and functional composition. There were significant spatial variations in water quality variables across the disturbance gradient (p <0.05). Highest mean temperature and suspended solids were recorded at the disturbed sites and lowest at undisturbed sites. Ephemeroptera, Plecoptera and Trichoptera (EPT) taxa dominated (70% in abundance) undisturbed sites while Diptera dominated (48% in abundance) at disturbed sites. Additionally, higher diversity and richness indices were recorded at undisturbed sites. Collectors were the dominant taxa at all sites with the abundance of shredders being highest at undisturbed sites. This study adds further evidence showing that land-use change from forestry to agriculture has a strong influence on the structural and functional composition of macroinvertebrates in Afrotropical streams.

A Coupled-Cavity Resonator Technique for Simultaneous Sensing of Dielectric Load and Position of Continuous Material Streams

An electromagnetic coupled-cavity resonator equipped with permanent insertion holes and designed to sense continuous dielectric material streams through the resonator is presented. The resonating structure comprises a pair of pill-box-shaped cylindrical cavities mutually coupled to each other through an aperture-loaded metal sheet of finite thickness. The input and output insertion holes in the top and bottom lids of the cavity structure form a channel for the flow of dielectric samples under test. The arrangement of aperture-coupled cavity sections results in antisymmetric and symmetric field distributions with split resonances. The resonating antisymmetric field is primarily utilized to detect dielectric load variations of the sample stream, similar to the commonly practiced permittivity based measurements in TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">010</sub> cavities. The additional resonance mode with the symmetric field distribution is more sensitive to position offsets of the sample in its concentric flow along the axis. Due to the added resonance, the arrangement provides for 2-D sensing of dielectric specimens under test (dielectric load variation and position offset) and improved accuracy can, thus, be achieved. The working principle of the coupled-cavity technique is analyzed qualitatively by numerical computations. The technique is validated by measuring samples of commercially available cotton fibers with a realized prototype.

Indirect Estimation of Flow and Suspended-sediment Concentration and Load in Small Mountain Streams: an Exploratory Study in Ribeira Seca Stream, Madeira Island

The aim of this study was to assess the applicability of indirect techniques for streamflow and suspended sediment concentration estimation and their use in the calculation of suspended sediment transport rate in the small mountain watersheds of Madeira Island, Portugal. Emphasis was given to the application of salt dilution gauging to the indirect determination of the flow rate and the use of water turbidity data to estimate the concentration of suspended sediments. The field and laboratory work carried out are briefly described, and the main experimental results and the field data from the short measurement campaign performed in the Ribeira Seca stream in Faial, on the north side of the island, are presented and discussed. Whilst the measurement campaign carried out was temporally and spatially limited, it was pioneering for Madeira and allowed to verify the applicability of the indirect hydrometric and sedimentometric techniques used in this exploratory study.

Loading of stream wood following the 2016 Chimney Tops 2 Wildfire: Great Smoky Mountains National Park, Tennessee, USA

AbstractLarge wood drives physical and ecological processes in river systems, but the relative roles of continuous individual tree mortality versus episodes of mass mortality in wood recruitment are not well understood. Here, the 2016 Chimney Tops 2 wildfire, a rare severe wildfire in the eastern United States, was used as a case study for examining the role of mass tree mortality in wood loads of streams in Great Smoky Mountains National Park (GSMNP), Tennessee. Wood surveys were conducted on four reaches in two drainage systems affected by the fire to ascertain the total frequency and volume of burned and unburned wood pieces and jams. Relative to unburned wood, the Chimney Tops 2 fire resulted in a major influx of burned wood to the study reaches, with large percentages of individual pieces (average of 47% by frequency, 48% by volume) and jams (average of 72% by frequency, 93% by volume) exhibiting burn marks. Burned wood pieces had a larger diameter than unburned pieces (p = .065). Results suggest that rare mass‐mortality events like the Chimney Tops 2 wildfire could play a major role in wood dynamics of mountain streams in humid forested regions.

High Rate Deposition in Cold Spray

Industrialization of cold spray introduces concerns regarding the cost and time efficiency of cold spray procedures. In this work, high rate deposition of tantalum was studied computationally and experimentally. Quasi-1D multiphase fluid simulations predicted minimal effects on the bonding conditions of particles with 5% to 14% increase in powder-to-gas mass flow ratio. Experimental specimens were produced to observe the mechanical and microstructural effects of increased powder stream loading. Adhesion and hardness tests as well as thermal conductivity, optical microscopy, and electron backscatter diffraction examinations only exhibited minor differences in the mechanical and microstructural properties of the specimens. The increased powder stream loading rate, however, allows a significant reduction in the time required for depositing the same amount of tantalum by a factor of three. The results of the study enable shorter cold spray deposition time. This leads to significant cost savings associated with consumption of helium and labor, while facilitating shorter turn-around times for repairing components and manufacturing of cold-sprayed products.

Baseflow nitrate dynamics within nested watersheds of an agricultural stream in Nebraska, USA

There is a need to evaluate high surface nitrate concentrations across agricultural watersheds, both spatially and temporally, to increase understanding of source and timing of nitrogen loads in streams and rivers. Bazile Creek is a high-nitrate stream originating in the agriculturally intensive Bazile Groundwater Management Area of Eastern Nebraska, USA. It is a gaining stream that receives groundwater with high nitrate concentrations originating from nonpoint sources. The objective of this study was to determine spatial and temporal variability of baseflow nitrate concentrations in Bazile Creek and its tributaries and to relate this variability to watershed characteristics. Surface-water nitrate samples were collected monthly from July 2018 through September 2019 from nine sites in the watershed and were analyzed for nitrate concentration. Average surface water nitrate-N concentrations within the watershed ranged from 2.7 to 15 mg L−1 and were significantly different between the sites (p < 0.05). Surface water nitrate-N concentrations varied seasonally in the main channel, recording the highest concentrations in winter (December-February, average = 14.4 mg L−1) when the discharge was minimum. High nitrate-N concentrations were observed in two of the five sampled tributaries, suggesting steady inputs of high-nitrate groundwater. The results of this study reveal substantial spatial variation in surface-water nitrate concentrations in the headwaters despite the close proximity of sampling sites. This study demonstrates that sampling tributaries along with the main channel of a stream is beneficial in determining nitrate inputs, variability and overall contaminant loading to a watershed.

Variability of annual sediment load and runoff in the Yellow River for the last 100 years (1919–2018)

The sediment load of the Yellow River, once the highest in the world, has decreased to a record low. The annual sediment load (ASL, t·yr−1) in the main stream of the Yellow River in the past 100 years (1919–2018) shows that the ASL was consistently high for the first 60 years and then decreased gradually until 1999, when the Green for Grain Project (GGP) launched on the Loess Plateau caused ASL to drop sharply. The annual runoff did not decrease as much as ASL from 1919 to 2018, while it decreased significantly in the middle reaches. With the construction of sediment storage dams, terraces, and reservoirs, especially after the GGP launched, the ASL of the Yellow River has been reduced to historic lows. For example, the annual average Normalized Difference Vegetation Index (NDVI) of the Yellow River Basin increased significantly from 1982 to 2016, and the ASL decreased exponentially with increasing NDVI. Although the annual precipitation has a stationary behavior in the Yellow River, the daily precipitation extremes affecting erosion showed an increase of 7% per degree of warming but did not change the trend of ASL reduction. Therefore, the effective management on the Loess Plateau can control the trend of the sediment load of the Yellow River. Erosion, sediment load, and runoff in changing environments are affected by flood control and drought resistance, so more attention should be paid to these hydrologic processes.

Design and development of a Python-based interface for processing massive data with the LOAD ESTimator (LOADEST)

LOADEST is a program for estimating constituent loads in rivers and streams developed by the U.S. Geological Survey (USGS), but it does not have a Graphical User Interface (GUI) that facilitates processing of large amounts of data. Therefore, we present the LOAD ESTimation (LOADEST) Parallel Data Processing Interface (LPDPI). LPDPI is unique as it features an easy-to-use workflow for data download and water quality estimations for numerous stations and multiple constituents and is readily applicable to any station with both flow and water quality data available. LPDPI incorporates a parallel module for faster load estimation and can identify and fix errors that occur while running LOADEST by adjusting calibration and estimation data inputs. LPDPI also includes an extension to extract and filter LOADEST output to facilitate further data analysis and use of the data to calibrate hydrologic models. The tool is a standalone executable for Windows and can be readily used without any additional packages or software installation.

Contrasting long-term trends of chloride levels in remote and human-disturbed lakes in south-central Ontario, Canada

Yao H, Paterson AM, James AL, McConnell C, Field T, Ingram R, Zhang D, Arnott SE, Higgins SN. 2020. Contrasting long-term trends of chloride levels in remote and human-disturbed lakes in south-central Ontrario, Canada. Lake Reserv Manage. XX:XXX–XXX. We examined a 41 yr data record from 4 monitored lakes in south-central Ontario, Canada, to demonstrate and explain long-term changes in chloride (Cl) loading and in-lake concentrations in relation to the degree of watershed disturbance. A mass balance calculation for each lake was used to determine ungauged shoreline loads. Correlations of lake Cl concentrations with each of 3 major contributing sources (inputs from inflowing streams, atmospheric deposition, and ungauged shoreline areas) revealed the contribution of each source to Cl trends at each lake. Areal loads (Cl load per year per unit area) showed the relative intensity of the contributions. Two lakes (Red Chalk, Plastic) with relatively undisturbed watersheds showed declining trends in atmospheric deposition, stream loads, lake export, and lake Cl concentrations, whereas 2 lakes (Harp, Dickie) with disturbed watersheds showed increased stream loads, lake export, and lake concentrations, despite long-term declines in atmospheric deposition. This contrasting trend was related to increased Cl concentrations in inflowing streams, which were caused by increased residential development and road salt applications. The ungauged shoreline loads in the disturbed watersheds made a contribution as high as 80% to total Cl loads. As increasing Cl concentrations have implications for aquatic biota, even at the relatively low concentrations observed in the study lakes, these findings highlight the need for improved management of road salt applications. Our results confirm that even relatively remote lakes within the Canadian Shield are potentially at risk from watershed disturbances that are disrupting the natural loading of Cl to inland waters.

In-stream oxygenation to mitigate internal loading of phosphorus in lowland streams

Many lowland regions are afflicted with episodic high phosphorus (P) concentrations in streams during low flow periods. It has been hypothesised that these P peaks are due to internal loading after reductive dissolution of ferric iron (Fe(III)) minerals in sediments with a high P/Fe ratio. Here, we experimentally tested that hypothesis by measuring the sediment/water fluxes of P in streams and by testing responses to in-stream oxygenation. A phosphate stock solution with a bromide (Br−) tracer was administered during 3 h in four streams with varying sediment P/Fe ratios during summer (low DO concentration). The experiment was repeated in winter (high DO concentration) in one of the streams. The sediments were either net P sinks (three cases), net unreactive (one case) or a net source (one case), with the net source occurring in the stream with the highest sediment P/Fe and at lowest DO concentration. A direct oxygenation experiment in one stream increased downstream DO concentration with about 1 mg O2 L−1 and decreased the P concentration with, on average, about 0.3 mg P L−1 over a two-week period. The efficiency of oxygenation to reduce P concentrations enhanced when flow rates were lower. In conclusion, this experimental study confirmed the hypothesis that internal P loading in streams is largest in high P/Fe sediments at low DO conditions. Lowering P concentrations in lowland streams should combine reduced P emission and strategies avoiding low DO concentration, i.e. reduced biological oxygen demand (BOD) and nutrient emissions.

Trends in nitrogen, phosphorus, and sediment concentrations and loads in streams draining to Lake Tahoe, California, Nevada, USA

Lake Tahoe, a large freshwater lake of the eastern Sierra Nevada in California and Nevada, has 63 tributaries that are sources of nutrients and sediment to the lake. The Tahoe watershed is relatively small, and the surface area of the lake occupies about 38% of the watershed area (1313 km2). Only about 6% of the watershed is urbanized or residential land, and as part of a plan to maintain water clarity, wastewater is exported out of the basin. The lake's clarity has been diminishing due to algae and fine sediment, prompting development of management plans. Much of the annual discharge and nutrient load to the lake results from snowmelt in the spring and summer months. To understand the relative importance of land use, climate, forest management, and other factors affecting trends in nutrient stream concentrations and loads, a Weighted Regression on Time Discharge and Season (WRTDS) model simulated these trends over a time frame of >25 years (mid-1970s to 2017). All studied locations generally show nitrate concentration and load trending down. Ammonium concentration and load initially trended down then increased continuously after 2005. Some locations show initially decreasing orthophosphate trends, followed by small significant increases in concentration and loads starting around 2000 to 2005. Total Kjeldahl nitrogen, total phosphorus and suspended sediment mostly trended downward. Overall, the trends in various forms of nitrogen were observed at most sites irrespective of the degree of development and indicate a change in ecological conditions is affecting the nitrogen cycle throughout the watershed, most likely attributable to forest aggradation and fire suppression. Ratios of bioavailable nitrogen in the form of nitrate and ammonium to orthophosphate have also trended downward during the period of record suggesting a shift of these streams from phosphorus limited to nitrogen limited.

Mercury and selenium loading in mountaintop mining impacted alkaline streams and riparian food webs

Coal is naturally enriched in trace elements, including mercury (Hg) and selenium (Se). Alkaline mine drainage from mountaintop mining valley fill (MTM-VF)—the dominant form of surface coal mining in Appalachia, USA—releases large quantities of Se into streams draining mined catchments, resulting in elevated bioaccumulation of Se in aquatic and riparian organisms. Yet, the release of Hg into these streams from MTM-VF has not yet been studied. We measured total Hg, methylmercury (MeHg), and Se in stream water, sediment, biofilm, cranefly larvae, and riparian spiders in alkaline streams (pH range 6.9–8.4) across a mining gradient (0–98% watershed mined) in central Appalachia. Hg concentrations ranged from below detection limit (BDL)-6.9 ng/L in unfiltered water, BDL-0.05 µg/g in bulk sediment, 0.016–0.098 µg/g in biofilm, 0.038–0.11 µg/g in cranefly larvae, and 0.046–0.25 µg/g in riparian spiders. In contrast to Se, we found that Hg concentrations in all environmental compartments were not related to the proportion of the watershed mined, suggesting that Hg is not being released from, nor bioaccumulating within, MTM-VF watersheds. We also did not find clear evidence for a reduction in Hg methylation or bioaccumulation under elevated Se concentrations: water, sediment, biofilm, and riparian spiders exhibited no relationship between Hg and Se; only cranefly larvae exhibited a negative relationship (p = 0.0002, r2 = 0.42). We suggest that the type of surface mining matrix rock, with resultant alkaline or acid mine drainage, is important for the speciation, mobility, and bioaccumulation of trace elements within watersheds affected by mining activities.

Beyond nitrogen and phosphorus subsidies: Pacific salmon (Oncorhynchus spp.) as potential vectors of micronutrients

Large quantities of material are moved annually from the ocean to freshwater systems by migrating Pacific salmon. Previous studies have focused on nitrogen and phosphorus provided by spawning salmon but largely ignored micronutrients essential to aquatic productivity. We collected salmon tissue, water, and biofilm from seven southeast Alaskan streams both before and during the salmon run to test for potential micronutrient provision by salmon and uptake by biofilm. To examine temporal patterns, one stream was also sampled with high frequency. Samples were analyzed using ICP-OES for boron (B), calcium (Ca), cobalt (Co), copper (Cu), iron (Fe), potassium (K), magnesium (Mg), manganese (Mn), molybdenum (Mo), sodium (Na), selenium (Se), silicon (Si), and zinc (Zn). Arrival of salmon increased stream water loads for Ca, Fe, Mg, and Na and the concentration of Co in biofilm across the seven study streams. Stream loads of B and biofilm Cu and Na content decreased in the presence of salmon. By examining one stream at finer temporal resolution, biofilm increased in Ca, Fe, and Mn concentrations near the end of the salmon run, indicating possible lag effects between peak salmon densities and biofilm micronutrient uptake. The increase in stream water micronutrient loads across space for four elements and uptake of three elements in biofilm through time suggest that salmon are a potential source of essential micronutrients for freshwater ecosystems, as has been repeatedly demonstrated for macronutrients. This study expands our understanding of resource subsidies by identifying potential micronutrients important to those ecological dynamics.