**1.1. Blackbird Creek Watershed**

positioning system (GPS), and geographic information system (GIS) technologies that provide a valuable tool for monitoring and assessing waterways in the Mid-Atlantic

**Keywords:** remote sensing, hyperspectral image, water quality, total suspended solids,

More than half of the United States population inhabits coastal and estuarine areas [1]. These regions are under pressure as rapid population growth, overutilization of natural resources, and removal of such resources as agriculture and urban development become more predominant. Although this growth and development provide economic opportunity, they also alter local ecosystems by changing land use and land cover; causing changes in soil and groundwater chemistry, watershed-level hydrology, and dissolved nutrients in waterways, particularly in the form of nitrogen and phosphorous species [2]. According to Nehrling [3], throughout the United States, commercial fertilizer use has experienced nearly a threefold increase, from approximately 6.8 million metric tons in 1960 to about 20.0 million metric tons in 2011 in order to accommodate rapid population growth and need for increased food

According to the National Oceanic and Atmospheric Administration (NOAA) National Ocean Service [4], estuaries have been seriously impacted by various anthropogenic activities and disturbances, and many are seriously degraded by pollution. Toxic substances such as chemicals and heavy metals, nutrient pollution (resulting in eutrophication), and pathogenic bacteria and viruses are the pollutants having the greatest impact on the health of estuarine waters [4]. Estuaries by their nature are transitional areas between the land and the sea including both freshwater and saltwater environments and have the accumulative impacts of both land and water activities. By far, large-scale changes from draining, filling, damming, or dredging are the greatest threats to estuaries [4]. These activities result in immediate destruction, loss

Given the increasing number of water quality issues such as harmful algal blooms (HABs) in economically significant waters of the world, methods are needed for early detection of these issues and their sources, which when used with other environmental and historic data can alert authorities a threatening condition. Remote sensing (RS) has the potential to provide accurate synoptic views of water quality conditions over a large spatial extent and can be used to estimate turbidity and algal biomass, and have the potential to identify algal taxonomic groups. Detection of water quality issues such as dominant algal taxonomic groups can provide coastal managers with information regarding those blooms that are potentially composed of harmful algae. As such, remote sensing is an important component of overall water quality and HAB-monitoring strategy. However, coastal and estuarine waters are optically complex and the monitoring of HABs is limited in these environments by remote

of estuarine habitats, or irreversible changes in the environment.

Estuaries.

170 Water Quality

**1. Introduction**

quantities.

sensing [5].

chlorophyll-*a*, turbidity

The Delaware Bay is where the Delaware terrestrial system meets the Delaware coastal waters, leading to complex and nonlinear-mixing processes of terrestrial and marine properties. However, scientists have little knowledge of many details of the biogeochemical cycles in the bay. Furthermore, biogeochemical variability in the Delaware Bay is affected by a number of processes occurring at a wide range of temporal and spatial scales. Considering the complex and dynamic nature of the Delaware Bay water, developing a sustainable monitoring system suitable for the varying scales of the processes occurring in this region is a difficult task, especially in response to catastrophic events and climate change.

As Stone [2] stated, between 2010 and 2014, the coastal state of Delaware has grown faster than the United States as a whole—4.2–3.3%, growth, respectively [17]. The Blackbird Creek Watershed is located in southern New Castle County, Delaware, and drains roughly 80 km2 and flows into the Delaware River just upstream from the Delaware Bay [18].

This largely semi-pristine forested watershed provides many recreational activities, and therefore varying degrees of anthropogenic effects disturb the ecosystem. Monitoring the Blackbird Creek Reserve has been on-going since mid-1970 for the detection of ecosystem changes and established management practices. Blackbird Creek is a part of the Delaware National Estuarine Research Reserve (DNERR) which is associated with the NOAA for maintaining the estuarine system. Just over a decade ago, the Delaware Department of Natural Resources and Environmental Control (DNREC) identified that roughly 36.1% of the watershed is designated for agricultural use, and an additional 13.2% for urban use [19]; **Figure 1**. However, based on more current data from the Delaware Geospatial Exchange, approximately 44% of the watershed is designated to agriculture and only about 4% to urban use.

**Figure 1.** Land use practices in Blackbird Creek, Delaware, as described by LSPC Model Segmentation (map copied from Stone 2016, map by DNREC [19].

The Blackbird Creek tidal marsh ecosystem is dominated by various salt marsh grasses and macro fauna. Similar to many estuaries in the United States, this ecosystem is threatened by the surrounding land-use activities especially agricultural and residential activities [12].

Stone [2] reported how population growth and land-use changes put pressure on ecosystems. As the population increases, more land is cleared for development and agricultural purposes. Increased impervious surfaces from roads, parking lots, and other infrastructure can prohibit rain from entering the soil system. This can result in the conversion of the rainfall to runoff, flowing into storm drains, rivers, and streams, and collecting sediments, harmful pollutants, and nutrients along the way. The monitoring of nutrient runoff into waterways and how nutrients are cycled through estuarine ecosystems are of particular importance in the Blackbird Creek Watershed. Rabalais et al. [20] and Boesch et al. [21] discussed how nutrient loading impacts streams, especially in large watersheds. Nutrients entering estuarine systems such as Blackbird Creek or the Choptank River often do so through both surface water and groundwater inputs. As Stone [2] reported, some agricultural practices, including over-tilling and unnecessary loosening of soil, over-irrigating cropland, and over-applying fertilizers, can send more soil particles and nutrients into the creek and, subsequently, into Mid-Atlantic Estuaries.

Delaware's agricultural land use has greatly impacted Delaware estuaries, in particular, poultry farming. Based on the report by the United States Department of Agriculture (USDA) cited by the News Journal [22], over 550 million broiler chickens were produced on the Delmarva Peninsula in 2012 alone, an increase of almost 14,000% since the early 1900s. According to the USDA National Agricultural Statistics Service [23], per year, Delaware state growers produced about 216 million birds alone. Poultry litter is overabundant as a by-product of the large chicken industry in the state of Delaware. Poultry litter is high in nutrients, particularly in phosphorous, and is often used as a fertilizer for pasture and hayfields throughout Delaware, including in the Blackbird Creek Watershed [24]. This litter contains high concentrations of water-soluble phosphorus and is readily transported as farm runoff. Excessive or improper fertilizer application can result in phosphorous buildup considering that the N:P ratio in plants is 8:1 while only 3:1 in poultry litter [25]. The United States Environmental Protection Agency (USEPA) identified phosphorous concentrations of 0.31 mg/L or greater to be detrimental to aquatic organisms, and is therefore the maximum value that should ever be in bioavailable form in waterways [26]. Studies have shown the detrimental impacts that phosphorous has on aquatic ecosystems, including eutrophication [27–29], mortalities of fish and invertebrates [30], and stream community shifts from a heterotrophic to an autotrophic state [31].

Major habitat change in the Blackbird Creek ecosystem is attributed to the abundance of invasive *P. australis*. Although invasive species are a less widely discussed human-caused disturbance in the watershed, it is by far the most noticeable one in the creek. Ozbay et al. [32] monitored potential impacts of *P. australis* invasion on aquatic species such as the blue crab population in Blackbird Creek Watershed to help understand the changing ecosystems in Delaware's coastal environment. Numerous studies have shown that *P. australis* invasions negatively impact essential fish habitats [33, 34]. Currently, it is not clear how invertebrates have responded to *P. australis* invasions. Research by Jivoff and Able [35] suggests that marsh surface vegetation influences the way blue crabs use marsh surface habitats. In the state of Delaware, *P. australis* is extensively studied, but most of these studies focus on the mechanism and prevention of *Phragmites*' invasion [36, 37]. Very few studies involved the detection and mapping of *P. australis* and its impact on fishery habitat in Delaware.
