Quantifying stream phosphorus dynamics and total suspended sediment export in forested watersheds in Vermont

Globally the quantity of reactive phosphorus (P) in soils, streams and groundwater has greatly increased throughout the 20th and early 21st centuries. This phenomenon is problematic in Vermont, evidenced by the repeated cyanobacteria blooms in shallow bays in Lake Champlain. While many studies have focused on P dynamics in agricultural watersheds, there is limited information on P dynamics in forested watersheds. Current remediation plans under the Lake Champlain total maximum daily loads (TMDL) call for substantial reductions in P loadings from forested areas of the basin. However, the lack of information and knowledge regarding forest P dynamics limits management and remediation plans. This study was conducted in three small forested watersheds, ranging in size from 2.5 to 8.3 square kilometers that have been managed under varying practices, including logging and maple sugaring. All three watersheds drain into Missisquoi Bay, a shallow bay in Lake Champlain that consistently has seasonal algal blooms. Streams in the forested watersheds were instrumented with turbidity sensors and pressure transducers to measure stage. A rating curve was developed during field visits to relate stage to discharge. Water samples were collected from May through November 2017 using ISCO Automated Samplers. A total of twenty storm events were captured, along with periodic baseflow sampling, and these data were used to characterize P concentrations and calculate seasonal P loadings. Results indicate that there is a strong positive relationship between turbidity, total suspended sediment and total phosphorus concentrations (R2 ranging from 0.64 to 0.83). The results of this project provide insight into transport of P and total suspended sediment within forested catchments of Lake Champlain tributaries. In particular, the research shows that fluxes in total phosphorus are linked to fluxes in total suspended sediment and that the overall monthly totals of P being exported from forested catchments are low, relative to urban, suburban and agricultural areas

Investigations of runoff production and sedimentation on forest roads

Forest roads constructed in steep mountain landscapes have been associated with a number of effects on hydrologic and geomorphic processes. This research examined the effects of forest roads on the flow of water and sediment in drainage basins in the Cascade range of western Oregon. A study conducted at the hillslope scale (< 0.1 km²) during the 1996 water year examined the factors controlling runoff production on forest roads. Runoff response was related to climatic conditions (storm size and soil moisture) and to the hillslope setting (size of the contributing hillslope, hillslope gradient, and soil depth on contributing hillslopes) on which roads were located. These observations were consistent with a theoretical model of runoff production on steep hillslopes. A study conducted at the large basin scale (181 km²) examined erosion associated with forest roads during the February 1996 flood. Roads functioned both as initiation sites for erosion and as depositional sites, interrupting the flow of water and sediment along hillslopes and in channels. Roads constructed prior to 1960 in midslope and valley floor positions experienced the highest frequency of erosion and deposition, and these impacts were concentrated at elevations below 800 m, where storm precipitation was augmented by snowmelt. Both fluvial and mass wasting processes deposited sediment on roads and eroded sediment from roads, and multiple processes were linked in complex cascades at many sites. Roads were a net source of sediment in the basins studied, although they functioned as both sources and storage sites for sediment, depending upon their location on hillslopes. The results point to the importance of roads in both modifying physical processes and in routing material through drainage basins. The findings have significant implications for the management of roads in forested landscapes

Effects of different soil media, vegetation, and hydrologic treatments on nutrient and sediment removal in roadside bioretention systems

Water quality performance of eight roadside bioretention cells in their third and fourth years of implementation were evaluated in Burlington, Vermont. Bioretention cells received varying treatments: (1) vegetation with high-diversity (7 species) and low-diversity plant mix (2 species); (2) proprietary SorbtiveMedia™ (SM) containing iron and aluminum oxide granules to enhance sorption capacity for phosphorus; and (3) enhanced rainfall and runoff (RR) to certain cells (including one with SM treatment) at three levels (15%, 20%, 60% more than their control counterparts), mimicking anticipated precipitation increases associated with climate change. A total of 121 storms across all cells were evaluated in 2015 and 2016 for total suspended solids (TSS), nitrate/nitrite-nitrogen (NOx), ortho-phosphorus (Ortho-P), total nitrogen (TN) and total phosphorus (TP). Heavy metals were also measured for a few storms, but in 2014 and 2015 only. Simultaneous measurements of flow rates and volumes allowed for evaluation of the cells’ hydraulic performances and estimation of pollutant load removal efficiencies and EMC reductions. Significant average reductions in effluent stormwater volumes (75%; range: 48–96%) and peak flows (91%; range: 86–96%) was reported, with 31% of the storms events (all less than 25.4 mm (1 in.), and one 39.4 mm (1.55 in.)) depth completely captured by bioretention cells. Influent TSS concentrations and event mean concentrations (EMCs) was mostly significantly reduced, and TSS loads were well retained by all bioretention cells (94%; range: 89–99%) irrespective of treatments, storm characteristics or seasonality. In contrast, nutrient removal was treatment-dependent, where the SM treatments consistently removed P concentrations, loads and EMCs, and sometimes N as well. The vegetation and RR treatments mostly exported nutrients to the effluent for those three metrics with varying significance. We attribute observed nutrient exports to the presence of excess compost in the soil media. Rainfall depth and peak inflow rate had consistently negative effects on all nutrient removal efficiencies from the bioretention cells likely by increasing pollutant mobilization. Seasonality followed by soil media presence, and antecedent dry period were other predictors significantly influencing removal efficiencies for some nutrient types. Results from the analysis will be useful to make bioretention designers aware of the hydrologic and other design factors that will be the most critical to the performance of the bioretention systems in response to interactive effects of climate change

The use of CMIP5 data to simulate climate change impacts on flow regime within the Lake Champlain Basin

Study region: Lake Champlain Basin, northwestern New England, USA. Study focus: Our study uses regional hydrologic analyses and modeling to examine alternative possibilities that might emerge in the Lake Champlain Basin streamflow regime for various climate scenarios. Climate data as well as spatial data were processed to calibrate the Regional Hydro-Ecological Simulation System (RHESSys) model runoff simulations. The 21st century runoff simulations were obtained by driving the RHESSys model with climate data from the Coupled Model Intercomparison Project phase 5 (CMIP5) for representative concentration pathways RCP 4.5 and 8.5. New hydrological insights for the region: Our analyses suggest that most of CMIP5 ensembles fail to capture both the trends and variability observed in historical precipitation when run in hindcast. This raises concerns of using such products in driving hydrologic models for the purpose of obtaining reliable runoff projections that can aid researchers in regional planning. A subset of five climate models among the CMIP5 ensembles have shown statistically significant trends in precipitation, but the magnitude of these trends is not adequately representative of those seen in observed annual precipitation. Adjusted precipitation forecasts project a streamflow regime described by an increase of about 30% in seven-day maximum flow, a four days increase in flooded days, a three orders of magnitude increase in base flow index, and a 60% increase in runoff predictability (Colwell index)

Runoff production on forest roads in a steep, mountain catchment

This study investigated how roads interact with hillslope flow in a steep, forested landscape dominated by subsurface flow and how road interactions with hillslope flow paths influence hydrologic response during storms in a second-order catchment. Runoff was measured continuously from 12 subcatchments draining to road segments and covering 14% of a 101-ha, second-order catchment (WS3) in the Andrews Forest, Oregon. Observed runoff over the 1996 water year was compared to predictions for runoff timing and interception of a hillslope water table based on a simple model of kinematic subsurface storm flow. Observed runoff behavior was consistent with model estimates, a finding that underscores the utility of this simple approach for predicting and explaining runoff dynamics on forest roads constructed on steep hillslopes. Road segments in the study area interacted in at least four distinct ways with complex landforms, potentially producing very different effects depending on landform characteristics. Hillslope length, soil depth, and cutbank depth explained much of the variation in road runoff production among subcatchments and among storm events. Especially during large storm events, a majority of instrumented road segments intercepted subsurface flow and routed it to ditches and thence directly to streams with a timing that contributed to the rising limb of the catchment-wide hydrograph. The approach used in this study may be useful for model development and for targeting road segments for removal or restoration

Identifying the spatial pattern and importance of hydro-geomorphic drainage impairments on unpaved roads in the northeastern USA

Roads have been widely studied as sources of runoff and sediment and identified as pollutant production sources to receiving waters. Despite the wealth of research on logging roads in forested, upland settings, little work has been conducted to examine the role of extensive networks of rural, low-volume, unpaved roads on water quality degradation at the catchment scale. We studied a network of municipal unpaved roads in the northeastern US to identify the type and spatial extent of ‘hydro-geomorphic impairments’ to water quality. We mapped erosional and depositional features on roads to develop an estimate of pollutant production. We also mapped the type and location of design interventions or best management practices (BMPs) used to improve road drainage and mitigate water quality impairment. We used statistical analyses to identify key controls on the frequency and magnitude of erosional features on the road network, and GIS to scale up from the survey results to the catchment scale to identify the likely importance of unpaved roads as a pollutant source in this setting. An average of 21 hydro-geomorphic impairments were mapped per kilometer of road, averaging 0.3 m3 in volume. Road gradient and slope position were key controls on the occurrence of these features. The presence of BMPs effectively reduced erosion frequency. Scaled up to the watershed and using a conservative estimate of road–stream connectivity, our results for the Winooski River watershed in the northeastern US suggest that roughly 16% and 6% of the average annual sediment and phosphorus flux, respectively, of the Winooski River may be derived from unpaved roads. Our study identifies an under-appreciated source of water quality degradation in rural watersheds, provides insights into identifying ‘hot spots’ of pollutant production associated with these networks, and points to effectiveness of design interventions in mitigating these adverse impacts on water quality. Copyright © 2017 John Wiley & Sons, Ltd

A New Machine-Learning Approach for Classifying Hysteresis in Suspended-Sediment Discharge Relationships Using High-Frequency Monitoring Data

Studying the hysteretic relationships embedded in high-frequency suspended-sediment concentration and river discharge data over 600+ storm events provides insight into the drivers and sources of riverine sediment during storm events. However, the literature to date remains limited to a simple visual classification system (linear, clockwise, counter-clockwise, and figure-eight patterns) or the collapse of hysteresis patterns to an index. This study leverages 3 years of suspended-sediment and discharge data to show proof-of-concept for automating the classification and assessment of event sediment dynamics using machine learning. Across all catchment sites, 600+ storm events were captured and classified into 14 hysteresis patterns. Event classification was automated using a restricted Boltzmann machine (RBM), a type of artificial neural network, trained on 2-D images of the suspended-sediment discharge (hysteresis) plots. Expansion of the hysteresis patterns to 14 classes allowed for new insight into drivers of the sediment-discharge event dynamics including spatial scale, antecedent conditions, hydrology, and rainfall. The probabilistic RBM correctly classified hysteresis patterns (to the exact class or next most similar class) 70% of the time. With increased availability of high-frequency sensor data, this approach can be used to inform watershed management efforts to identify sediment sources and reduce fine sediment export

Estimation of the water balance of for a small tropical andean catchment

The present study seeks to estimate the water balance for a tropical catchment in the Andes of Ecuador. Temporal variation in precipitation and temperature of the Chaquilcay microcatchment were studied; it is a natural ecosystem situated in the Aguarongo Protected Forest in Gualaceo, Ecuador. Four meteorological stations of the National Institute of Meteorology and Hydrology (INAMHI-Instituto Nacional de Meteorología e Hidrología) were studied for 33 years (1982-2015), in order to quantify the contributions and losses of water, and statistical analyzes of the time series. To fill and validate the series of precipitation and temperature, a double mass analysis was used to develop reference stations and fill missing records. Temperature data were supplemented with the isothermal raster of Ecuador. A digital elevation model (DEM) was used to predict the amount of sun light, and the Thornthwaite method (1948) was applied to estimate time series of evapotranspiration. Our water balance analysis indicates 843;7 mm of total annual precipitation, a storage difference of 18;71 mm representing 2;22% of the total annual precipitation, surplus of 144;5 mm, and current evapotranspiration of 680;5 mm, amounting to 17;13% and 80;65% of the total annual precipitation, respectively

ESTIMACIÓN DEL BALANCE HÍDRICO DE UNA CUENCA ANDINA TROPICAL

El presente estudio estima el balance hídrico para una cuenca tropical en los Andes de Ecuador. Se estudió la variación temporal de la precipitación y la temperatura de la microcuenca Chaquilcay, ecosistema natural situado dentro del Bosque y Vegetación Protector Aguarongo en Gualaceo, Ecuador. Para examinar la variabilidad temporal de la temperatura y la precipitación, se estudiaron cuatro estaciones meteorológicas del Instituto Nacional de Meteorología e Hidrología (INAMHI) durante el periodo 1982 a 2015. Para cuantificar las contribuciones y pérdidas de agua, se llevaron a cabo análisis estadísticos de las series temporales. Mientras que, para llenar y validar las series de precipitación y temperatura, se utilizó un análisis de doble masa desarrollando estaciones de referencia y con ello completar los registros faltantes. Los datos de temperatura se complementaron con la trama isotérmica del Ecuador. Además, se usó un modelo de elevación digital (MED) para predecir la cantidad de luz solar y se aplicó el método de Thornthwaite (1948) para estimar series temporales de evapotranspiración. El análisis de balance hídrico indica 843;7 mm de precipitación anual total, una diferencia de almacenamiento de 18;71 mm que representa el 2;22% de la precipitación anual total, un excedente de 144;5 mm y una evapotranspiración real de 680;5 mm, que asciende a 17;13% y 80;65% del total anual de precipitación, respectivamente.// The present study seeks to estimate the water balance for a tropical catchment in the Andes of Ecuador. Temporal variation in precipitation and temperature of the Chaquilcay microcatchment were studied; it is a natural ecosystem situated in the Aguarongo Protected Forest in Gualaceo, Ecuador. Four meteorological stations of the National Institute of Meteorology and Hydrology (INAMHI - Instituto Nacional de Meteorología e Hidrología) were studied for 33 years (1982-2015), in order to quantify the contributions and losses of water, and statistical analyzes of the time series. To fill and validate the series of precipitation and temperature, a double mass analysis was used to develop reference stations and fill missing records. Temperature data were supplemented with the isothermal raster of Ecuador. A digital elevation model (DEM) was used to predict the amount of sun light, and the Thornthwaite method (1948) was applied to estimate time series of evapotranspiration. Our water balance analysis indicates 843;7 mm of total annual precipitation, a storage difference of 18;71 mm representing 2;22% of the total annual precipitation, surplus of 144;5 mm, and current evapotranspiration of 680;5 mm, amounting to 17;13% and 80;65% of the total annual precipitation, respectively

Optimizing wetland restoration to improve water quality at a regional scale

Published by IOP Publishing Ltd. Excessive phosphorus (P) export to aquatic ecosystems can lead to impaired water quality. There is a growing interest among watershed managers in using restored wetlands to retain P from agricultural landscapes and improve water quality. We develop a novel framework for prioritizing wetland restoration at a regional scale. The framework uses an ecosystem service model and an optimization algorithm that maximizes P reduction for given levels of restoration cost. Applying our framework in the Lake Champlain Basin, we find that wetland restoration can reduce P export by 2.6% for a budget of $50 M and 5.1$200 M. Sensitivity analysis shows that using finer spatial resolution data for P sources results in twice the P reduction benefits at a similar cost by capturing hot-spots on the landscape. We identify 890 wetlands that occur in more than 75% of all optimal scenarios and represent priorities for restoration. Most of these wetlands are smaller than 7 ha with contributing area less than 100 ha and are located within 200 m of streams. Our approach provides a simple yet robust tool for targeting restoration efforts at regional scales and is readily adaptable to other restoration strategies