Brian S. Caruso

Temporal and spatial patterns of extreme low flows and effects on stream ecosystems in Otago, New Zealand

Abstract The temporal and spatial patterns of summer extreme low flows and effects on stream ecosystems were evaluated throughout the Otago Region of the South Island of New Zealand during a severe drought in 1998–1999. Flows, water quality, and aquatic biology were monitored bimonthly at 12 locations as part of a long-term regional monitoring programme and results were evaluated and compared among summer 1998–1999 and all previous summers, as well as among three major subregions. Flows during the drought were extremely low for prolonged periods in many locations, particularly in North Otago. At most sites temperatures were slightly higher for a longer period than during other summers. In predominantly agricultural/pastoral catchments, widespread bacterial contamination of streams occurred due to increased livestock use of watercourses and decreased dilution during low flows. Concentrations of other contaminants derived from non-point sources, including nitrogen, phosphorus, and sediment, decreased in many locations due to the lack of rainfall and runoff events. Electrical conductivity generally increased as a result of the lack of dilution and increased evaporation and groundwater inputs. Overall water quality was worst in agricultural catchments in South Otago, and returned to conditions prior to the low flows by late autumn in most areas. The diversity of benthic macroinvertebrate communities and number of sensitive taxa decreased somewhat in many locations, but the magnitude and duration of these effects were not great. Differences between summer 1998–1999 and other periods, and among subregions, were not significant. Although some differences in low flows and effects on stream ecosystems across a range of landscapes and catchments can occur, the rapid recovery of water quality and benthic macroinvertebrates in most locations indicates that many streams are resilient to extreme low flows and drought with minor long-term effects.

Quantifying changes in flooding and habitats in the Tonle Sap Lake (Cambodia) caused by water infrastructure development and climate change in the Mekong Basin

The economic value of the Tonle Sap Lake Floodplain to Cambodia is arguably among the highest provided to a nation by a single ecosystem around the world. Nonetheless, the Mekong River Basin is changing rapidly due to accelerating water infrastructure development (hydropower, irrigation, flood control, and water supply) and climate change, bringing considerable modifications to the flood pulse of the Tonle Sap Lake in the foreseeable future. This paper presents research conducted to determine how the historical flooding regime, together with human action, influenced landscape patterns of habitats in the Tonle Sap Lake, and how these habitats might shift as a result of hydrological changes. Maps of water depth, annual flood duration, and flood frequency were created for recent historical hydrological conditions and for simulated future scenarios of water infrastructure development and climate change. Relationships were then established between the historical flood maps and land cover, and these were subsequently applied to assess potential changes to habitat cover in future decades. Five habitat groups were clearly distinguishable based on flood regime, physiognomic patterns, and human activity: (1) Open water, flooded for 12 months in an average hydrological year; (2) Gallery forest, with flood duration of 9 months annually; (3) Seasonally flooded habitats, flooded 5-8 months and dominated by shrublands and grasslands; (4) transitional habitats, flooded 1-5 months and dominated by abandoned agricultural fields, receding rice/floating rice, and lowland grasslands; and (5) Rainfed habitats, flooded up to 1 month and consisting mainly of wet season rice fields and village crops. It was found that water infrastructure development could increase the area of open water (+18 to +21%) and the area of rainfed habitats (+10 to +14%), while reducing the area covered with seasonally flooded habitats (-13 to -22%) and gallery forest (-75 to -83%). Habitat cover shifts as a result of climate change include a net increase of open water (2-21%), as well as a reduction of rainfed habitats by 2-5% and seasonally flooded habitats by 5-11%. Findings from this study will help guide on-going and future conservation and restoration efforts throughout this unique and critical ecosystem.

Regional river flow, water quality, aquatic ecological impacts and recovery from drought

Abstract During severe drought and low flows in the Otago Region of the South Island of New Zealand, increased bacterial contamination of rivers occurred in agricultural/pastoral catchments due to greater stock use of waterways and the lack of dilution and flushing flows. Concentrations and loadings of nitrogen and phosphorus generally decreased due to the lack of rainfall, runoff and transport from diffuse sources. Other analytes, including dissolved solids and pH, did not change to any considerable degree and were quite spatially variable. Although the health of benthic macroinvertebrate communities can decrease with a lower diversity and fewer sensitive taxa, effects were not significant in most rivers. Algal blooms occurred in some locations, particularly in lowland agricultural catchments with low water velocities and little shade. The prolonged lack of flushing flows can be a significant problem. Fish kills occurred where they became stranded and isolated from the main flow and where there was a lack of deeper pool refuges. Temperatures in excess of 25°C can also result in isolated fish kills, but the duration of these high temperatures appears to be the most critical factor. Adverse effects from drought can be widespread and severe in some locations, but appear to be relatively short-lived with recovery occurring rapidly with increasing flows at most locations. This indicates a degree of resilience of rivers to drought and low flows with long-term impacts that are not severe.

Spatial and temporal variability of stream phosphorus in a New Zealand high‐country agricultural catchment

Abstract Spatial and temporal variability of stream total phosphorus (TP) concentrations and loadings was evaluated over a year in a high‐country agricultural catchment. One storm event was also sampled at the inflow to a lake. An upland tributary had the highest median concentration (0.064 mg 1‐1), but the maximum (0.614 mg 1‐1) occurred at the inflow during the storm. Values near the lake surface were low but increased with depth in summer. There was a large difference between two streams, and values exceeded water quality guidelines in several locations. Seasonality in concentrations was not evident. Mean and median loadings at the inflow were approximately 7000 and 680 g day‐1, respectively, and the maximum was 81 540 g day‐1during the storm. TP loadings to the lake during a synoptic survey were 470 g day‐1 or 13 g km‐2day‐1. The lower half of the catchment contributed 72% of the loading to the lake. Baseflow, snowmelt, and one storm accounted for 47%, 30%, and 23%, respectively, of the total annual loading. Fertiliser, livestock waste, and trampling of stream banks by livestock contribute to the problem and can be minimised though use of best management practices in areas identified in this study.

Flood modelling in a high country mountain catchment, New Zealand: comparing statistical and deterministic model estimates for ecological flows

Abstract Statistical and deterministic modelling estimates of flood magnitudes and frequencies that can affect flood-plain ecology in the upper Ahuriri River catchment, a mountainous high country catchment in the New Zealand Southern Alps, were evaluated. Statistical analysis of 46 years of historical data showed that floods are best modelled by the generalized extreme value and lognormal distributions. We evaluated application of the HEC-HMS model to this environment by modelling flood events of various frequencies. Model results were validated and compared with the statistical estimates. The SCS curve number method was used for losses and runoff generation, and the model was very sensitive to curve number. The HEC-HMS flood estimates matched the statistical estimates reasonably well, and, over all return periods, were on average approximately 1% greater. However, the model generally underestimated flood peaks up to the 25-year event and overestimated magnitudes above this. The results compared well with other regional estimates, including studies based on L-moments, and showed that this catchment has smaller floods than other similarly-sized catchments in the Southern Alps. Editor D. Koutsoyiannis; Associate editor H. Aksoy Citation Caruso, B.S., Rademaker, M., Balme, A., and Cochrane, T.A., 2013. Flood modelling in a high country mountain catchment, New Zealand: comparing statistical and deterministic model estimates for ecological flows. Hydrological Sciences Journal, 58 (2), 328–341.

WATER QUALITY SIMULATION FOR PLANNING RESTORATION OF A MINED WATERSHED

Water quality simulation was performed to evaluate the effects of restoration alternatives on metals transport in a mountainous watershed in Montana, U.S.A. impacted by hundreds of abandoned hardrock mines. The Water Quality Analysis Simulation Program (WASP5), developed by the U.S. Environmental Protection Agency (U.S. EPA), was used to assist in planning restoration of the Upper Tenmile Creek watershed, a major drinking water supply for the City of Helena. Synoptic survey data collected by U.S. EPA and the U.S. Geological Survey were used for model calibration and validation. The effectiveness of eight restoration alternatives was modeled under steady-state, low flow conditions. These alternatives ranged from removal of adit and point source discharges to modification of the water supply scheme to provide higher in-stream flows. The model was also used for a number of related purposes, including evaluation of metals loadings and losses, exceedances of water quality standards, interactions between metals in water and bed sediment, and model and data uncertainties. Although standards exceedances are common throughout the watershed, modeling results indicated that removal of point sources, mine waste near watercourses, and streambed sediment can help improve water quality. Alteration of the water supply scheme and increasing baseflow will also ultimately be required to meet standards for all metals. The model also showed that although adits and point sources contribute significant metals loadings to the stream during baseflow, in some areas shallow groundwater and bed sediment can also be sources of metals. Adsorption and precipitation onto bed sediments are also important loss mechanisms in some locations. The model helped to identify uncertainties in the metal partition coefficients associated with sediment, significance of precipitation reactions, and locations of unidentified sources and losses of metals.

Attributes and uncertainty of dissolved zinc data from a mined catchment

This study evaluated the attributes and uncertainty of non-point source pollution data derived from synoptic surveys in a catchment affected by inactive metal mines in order to help to identify and select appropriate methods for data analysis/reporting and information use. Dissolved zinc data from the Upper Animas River Basin, Colorado, USA, were the focus of the study. Zinc was evaluated because concentrations were highest relative to national water quality criteria for brown trout, and zinc had the greatest frequency of criteria exceedances compared with other metals. Data attributes evaluated included measurement and model error, sample size, non-normality, seasonality and uncertainty. The average measurement errors for discharges, concentrations and loadings were 0·15, 0·1 and 0·18, respectively. The 90 and 95% coefficients of confidence intervals for mean concentrations based on a sample size of four were 0·48 and 0·65, respectively, and ranged between 0·15 and 0·23 for sample sizes greater than 40. Aggregation of data from multiple stations decreased the confidence intervals significantly, but additional aggregation of all data increased them as a result of increasing spatial variability. Unit area loading data were approximately log-normal. Concentration data were right-skewed but not log-normal. Differences in median concentrations were appreciable between snowmelt and both storm flow and baseflow, but not between storm flow and baseflow. Differences in unit area loadings between all flow events were large. It was determined that the average concentration and unit area loading values should be estimated for each flow event because of significant seasonality. Time weighted values generally should be computed if annual information is required. The confidence in average concentrations and unit area loadings is dependent on the computation method used. Both concentrations and loadings can be significantly underestimated on an annual basis when using data from synoptic surveys if the first flush of contaminants during the initial snowmelt runoff period is not sampled. The ambient standard for dissolved zinc for all events was estimated as 1600 μg l−1 using the 85th percentile of observed concentration data, with a 90% confidence interval width of 200 μg l−1. Copyright

Connectivity and Jurisdictional Issues for Rocky Mountains and Great Plains Aquatic Resources

Understanding the connectivity between wetlands and headwater intermittent and ephemeral streams with downstream navigable waters has become a critical focus for U.S. Clean Water Act protection. Recent Supreme Court decisions resulted in a new interpretation and federal agency guidance for how to assess jurisdiction over waters of the U.S. under Section 404 (dredge and fill permits). For jurisdictional determinations (JDs) of waters considered to be ‘geographically isolated’ or requiring an evaluation of their ‘significant nexus’ to navigable waters, coordination between the U.S. Environmental Protection Agency (EPA) and Army Corps of Engineers (COE) is required. EPA Region 8 evaluated all coordinated JDs during the first year of guidance implementation from June 2007 to June 2008. The region includes the Rocky Mountains, Great Plains, and parts of the Colorado Plateau, including portions of 20 Level III Ecoregions. Approximately 54% of all stream miles are 1st-order channels, and 77% are intermittent. During the period, JDs for 1,265 individual waters from three COE districts were evaluated, resulting in 793 wetlands, 12 streams, and 18 water bodies considered non-jurisdictional due to isolation. Significant nexus evaluation was required for 441 waters, of which 49 wetlands, 66 streams and 14 other water bodies were considered non-jurisdictional.

Impacts of groundwater metal loads from bedrock fractures on water quality of a mountain stream

Acid mine drainage and metal loads from hardrock mines to surface waters is a significant problem in the western USA and many parts of the world. Mines often occur in mountain environments with fractured bedrock aquifers that serve as pathways for metals transport to streams. This study evaluates impacts from current and potential future groundwater metal (Cd, Cu, and Zn) loads from fractures underlying the Gilt Edge Mine, South Dakota, on concentrations in Strawberry Creek using existing flow and water quality data and simple mixing/dilution mass balance models. Results showed that metal loads from bedrock fractures to the creek currently contribute <1% of total loads. Even if background water quality is achieved upstream in Strawberry Creek, fracture metal loads would be <5%. Fracture loads could increase substantially and cause stream water quality standards exceedances once groundwater with elevated metals concentrations in the aquifer matrix migrates to the fractures and discharges to the stream. Potential future metal loads from an upstream fracture would contribute a small proportion of the total load relative to current loads in the stream. Cd has the highest stream concentrations relative to standards. Even if all stream water was treated to remove 90% of the Cd, the standard would still not be achieved. At a fracture farther downstream, the Cd standard can only be met if the upstream water is treated achieving a 90% reduction in Cd concentrations and the median stream flow is maintained.

Agricultural Diffuse Nutrient Pollution Transport in a Mountain Wetland Complex

Wetlands in mountain environments provide critical ecosystem services but are increasingly threatened by agricultural land use intensification. This study evaluates agricultural nonpoint source nutrient pollution transport in a wetland–stream–lake complex in a mountain, tussock grassland catchment in the South Island, New Zealand. Flow and water-quality monitoring in the Lake Clearwater catchment during three flow events from May to August 2010 (autumn high flow, winter low flow, and winter high flow) showed high concentrations and exceedances of water quality guidelines for total nitrogen (TN) and total phosphorus (TP) in small ephemeral streams draining agricultural land during high flows. Concentrations were attenuated through the wetlands to below guidelines, with the exception of TN which still remained slightly higher. Most TN was in the organic form above and below the wetland, suggesting N sources from animal waste/agricultural land and organic material and vegetation within the wetland. Most TP was particulate associated with suspended solids during high flows. Dissolved forms of N and P generally were below guidelines. Flows and loads (instantaneous and daily) increased at the lake outlet during winter high flow, indicating unaccounted sources to the lake from groundwater, the wetlands, or the lake sediments, and seasonal N saturation. Infiltration losses to shallow groundwater along the main perennial tributary likely re-appear as discharge to the wetlands and lake downstream. Surface–groundwater interactions play a dominant role in N transport to the wetland complex due to highly permeable soils and glacial alluvial deposits. Loads and unit loads of TN and TP were also elevated in the ephemeral streams. Results show that TN and TP concentrations and unit loads during high flows in ephemeral streams in this mountain grassland catchment are similar to, or higher than, values for impacted lowland pasture catchments. Although impacts to the wetland ecosystem have not been observed to date, the lake is shifting toward a mesotrophic state, and further research is needed to elucidate impacts of nutrient loads and help meet conservation and restoration goals.