Advances in Watershed Science and Assessment

Accurate and detailed land use and land cover information forms an important resource for hydrologic analysis; remote sensing forms a critical resource for acquiring and analyzing broad-scale land use information. Although aerial photography is an important resource for land use information, it was the availability of multispectral satellite data beginning in 1972 that significantly advanced the ability of remote sensing researchers to systematically monitor and evaluate land use/land cover changes and their impacts on water quality and quantity. In that context, practitioners developed classification schemes specifically tailored for use with remotely sensed imagery and for systematic assessment of land use change. Since then, land observation technologies have evolved to allow extensive and intricate land use monitoring techniques, and now, in the twenty-first century, include the use of lasers for 3-D analyses and unmanned aerial systems. Such technologies have enabled land use assessment to contribute not only to its original focus in urban and regional planning but to a broad range of environmental and social issues. This chapter provides an overview of remote sensing, its technological evolution, and remote sensing applications in land use and land cover mapping and monitoring, with a focus upon implications for watershed assessment and management.

Life on Earth depends on water. Yet water resources are severely stressed by the rapid growth of the human population and activities. In arid environments the exploration and monitoring of water resources is a prerequisite for water accessibility and rational use and management. To survey large arid areas for water, conventional land-based techniques must be complemented by using satellite and airborne remote sensors. Surface water systems can be mapped using multispectral and radar sensors; soil moisture in the unsaturated zone can be remotely sensed with microwave radiometers using indirect indicators, such as microwave emissivity; freshwater wetlands can be mapped using multispectral cameras; and freshwater springs can be detected using thermal infrared radiometers. Satellite remote sensors and satellite gravitational surveys can be used in combination with ancillary data analysis to infer groundwater behavior from surface expressions and to estimate groundwater aquifer storage. This chapter provides an overview of satellite and airborne remote sensing techniques for managing water resources and monitoring drought in arid and semiarid regions.

Airborne imaging spectrometry is a powerful tool to investigate key biophysical parameters in inland waters. High spectral resolution data forms a contiguous spectrum that enables the detection and identification of a variety of key water quality indicators (e.g. cyanobacteria pigments). High spatial resolution imagery is suitable for fine-scale observation (e.g. the patchy spatial distribution of phytoplankton in productive waters). Airborne observations ensure flexible flight paths that allow observations of unexpected events to be acquired promptly. In this chapter, we present an overview of remote sensing techniques, by focusing on imaging spectrometry, for assessing water quality parameters in inland waters such as lakes, streams, rivers, reservoirs and ponds (defined ‘Case-2 waters’ according to a traditional remote sensing terminology). Then, we present examples of applications by using airborne Multispectral Infrared and Visible Imaging Spectrometer (MIVIS) images of Italian inland waters acquired at a spatial resolution varying from 3 to 5 m. Those examples include the retrieval of water quality parameters (i.e. chlorophyll-a, suspended particulate matter and coloured dissolved organic matter), the detection and monitoring of submerged vegetation, the observation of a cyanobacteria bloom in productive lakes and the investigation of the signal reflected by floating materials of terrestrial origin (i.e. pollens and oil).

An integrated assessment of water quality stressors at watershed scale is the basis for timely and effective management actions. The capacity of remote sensing to deliver spatial and temporal information about fundamental environmental dynamics makes it an ideal tool for determining the causes of water quality deterioration. This chapter focuses on harmful algal blooms in Lake Taihu (China), as a case study, demonstrating the potential of remote sensing for integrated assessment of watershed dynamics. The temporal and spatial variability of the conditions in Lake Taihu and its watershed were derived from satellite data to produce a monthly time series of algal bloom coverage, aquatic vegetation extent, and land cover from 2000 to 2013. Environmental features related to nutrient loading, climate conditions, and agricultural practices were also used to analyze the driving forces of algal blooms. Two distinct temporal patterns were identified. Prior to 2006, bloom initiation date was sensitive to agricultural activities (winter crop productivity and nutrient loading). After 2006–2007, an inversion of this relationship was observed, suggesting nutrient saturation with a shift to other watershed scale stressors, mainly climate related. After 2009, a return to pre-2006 conditions was shown. These results demonstrate how remote sensing can be used to monitor watershed dynamics as a whole, especially in conjunction with in situ environmental data.

Remote, satellite-based sensing is a cost-effective way to gather information needed for regional water quality assessments in lake-rich areas. A major advantage is that it enables retrieval of current and historic information on lakes that were not part of ground-based sampling programs. Advances over the past decade have enabled the use of satellite imagery for regional-scale measurement of lake characteristics, such as clarity and chlorophyll. For example, in the Midwest USA, historic and recent Landsat water clarity assessments have been conducted on more than 20,000 lakes to investigate spatial and temporal patterns and explore factors that affect water quality. The spatial characteristics of Landsat imagery allow for the assessment of all lakes larger than ~4 ha, but the broad nature and placement of its spectral bands have limited assessments largely for water clarity. European Space Agency (ESA) MERIS imagery with spectral bands that were selected for water has been used to assess chlorophyll for about 900 of Minnesota’s large lakes (those > 150 ha). Improvements of the recently launched Landsat 8 and upcoming ESA Sentinel-2 satellites will expand our capabilities further enabling assessment of other optically related water quality characteristics, such as chlorophyll, colored dissolved organic matter (CDOM), and mineral suspended solids for all lakes, and upcoming Sentinel-3 will continue these capabilities for large lakes.

Human water use around the globe continues to increase while available water supplies are threatened by contamination, climate change, and aging infrastructure. Effective management of water resources is essential to ensure that water is available when and where it is needed. A necessary first step is quantifying the amount of water needed and making this information readily available to decision-makers. Specifically, information is needed on both the total amount of water withdrawn and the portion of that water which is not returned to the source, at a spatial and temporal scale that will support management decisions. Quantifying this water loss (i.e., consumptive use) is important for gauging impacts to downstream water users and to maintaining functioning ecosystems. This effort can be challenging in large basins where water use data may be collected in various formats by numerous agencies utilizing different metrics. The objective of this chapter is to present a case study model developed for the Potomac River Basin in the United States. The model consists of a basin-wide analysis and mapping tool that incorporates monthly water use data from multiple political jurisdictions, estimates consumptive water use, displays raw and summary information in an interactive geospatial format, and shares information with stakeholders via an interactive web-based mapping tool. The developed tool is expected to assist in long-term local, state, and basin-wide comprehensive water resources planning; real-time drought management; and a better understanding of human impacts on water resources.

Measurements of natural water quality and water quantity are essential to make informed decisions for sustainable management of water resources and ecosystem protection. During the late nineteenth and early twentieth centuries, manual or discrete water monitoring techniques were developed and refined for water quality and quantity measurements, and many of these techniques are still used around the world. Discrete water quantity measurements and water quality sampling are conducted at regular time intervals (e.g., monthly) and do not provide sufficient data to capture temporal and spatial changes that occur during episodic events. In recent decades, there have been significant advances in water monitoring technologies that include sensor technologies, remote monitoring technologies, and data transfer technologies. These technologies allow water resource managers and researchers to capture real-time water quantity and quality data during episodic events such as major storms. Real-time and continuous water monitoring can capture temporal changes and provides broader spatial coverage of water quantity and quality in a watershed. Furthermore, it allows data collection when it is normally impractical with discrete sampling (e.g., during major storm events, nighttime, remote, and dangerous locations). This chapter presents an overview of advances in water sensor technologies. Topics discussed include various types of sensors for water quantity and water quality measurements, examples of commercially available water quantity and water quality monitoring devices, data collection and transport platforms, and data management and quality assurance/quality control for water monitoring.

Karst aquifers are productive groundwater systems, supplying approximately 25 % of the world’s drinking water. Sustainable use of this critical water supply requires information about rates of recharge to karst aquifers. The overall goal of this project is to collect long-term, high-resolution hydrologic and geochemical datasets at James Cave, Virginia, to evaluate the quantity and quality of recharge to the karst system. To achieve this goal, the cave has been instrumented for continuous (10-min interval) measurement of the (1) temperature and rate of precipitation; (2) temperature, specific conductance, and rate of epikarst dripwater; (3) temperature of the cave air; and (4) temperature, conductivity, and discharge of the cave stream. Instrumentation has also been installed to collect both composite and grab samples of precipitation, soil water, the cave stream, and dripwater for geochemical analysis. This chapter provides detailed information about the instrumentation, data processing, and data management; shows examples of collected datasets; and discusses recommendations for other researchers interested in hydrologic and geochemical monitoring of cave systems. Results from the research, briefly described here and discussed in more detail in other publications, document a strong seasonality of the start of the recharge season, the extent of the recharge season, and the geochemistry of recharge.

Bioassessment can be broadly defined as the use of biota to assess the nature and magnitude of anthropogenic impacts to natural systems. We focus on an important and specific type of bioassessment: the use of ecological assemblages, primarily fish, macroinvertebrates, and algae, as indicators of anthropogenic impairment in aquatic systems. Investigators have long known that biota provide spatially and temporally integrative indicators of impairment. This chapter provides an introduction to the process of developing assemblage-level indices that provide quantitative estimates of the ecological integrity of freshwater ecosystems. We discuss important developments made in the latter half of the twentieth century which are still relevant and useful for bioassessment, as well as more recent developments that have improved the effectiveness of bioassessment strategies. Throughout the chapter, we focus on analytical approaches for improving the effectiveness of bioassessment indices for detecting anthropogenic impairment. In the concluding section of the chapter, we widen our perspective and include excerpts from discussions with three expert practitioners on topics that are more broadly applicable to the assessment of the ecological integrity of aquatic systems. The major challenge for all bioassessment programs is to separate the effects of anthropogenic impairment on biota from the effects of natural environmental variability unrelated to impairment. Analytical developments, such as advanced predictive modeling techniques, coupled with emerging technologies and the development of large-scale bioassessment programs will continue to increase our ability to meet this challenge and to improve our understanding of how aquatic assemblages are affected by anthropogenic impairment.

Microbial source tracking (MST) is a still-new and developing discipline that allows users to discriminate among the many potential sources of fecal pollution in environmental waters. As MST continues to transition from the realm of research to that of application, it is being widely used in beach monitoring, total maximum daily load (TMDL) assessment of pollution sources, and any other waters that do not meet designated use criteria as determined by high densities of fecal indicator bacteria (FIB). The main area of research activity in MST focuses on the identification of source-specific genetic markers that can be used to detect contributions from different hosts such as humans, livestock, and wildlife. However, a variety of other accessible approaches can also be used including detailed investigations of the watershed and infrastructure, chemical tracers and leak tests, and increased FIB sampling. This chapter can serve as a guide for decision-making on where, when, and how to deploy MST. Included are discussions of the main drivers of MST and how these have shaped the development of past and present methodological approaches, plus current research initiatives such as community analysis that could usher in yet another new and improved methodological basis for the entire field of MST. Finally, a tiered system is presented as a recommended means to navigate the multiple options for MST analyses that will assist the reader in how best to use MST within the context of more traditional approaches.