Chapter 2 – State of the Bay, Third Edition

CHAPTER 2 – STATE OF THE BAY, THIRD EDITION Galveston Bay: An Overview of the System Written & Revised by L. James Lester Ecosystems are open systems, that is, things are constantly entering and leaving, even though the general appearance and basic functions may remain constant for long periods of time. —E. P. Odum, Ecology and Our Endangered Life Support Systems, 1989 Introduction Galveston Bay is a tremendous recreational, economic, and environmental asset to Texas and the nation.1 To properly manage human activities that affect this ecosystem, it is necessary to understand the system’s composition, the processes that link its components, and how it interacts with its environs. Figure 2.1. Sunset on Galveston Bay. Image courtesy ©2006 This bay is a complex, iStockphoto.com/Dave Huss. interconnected system of biological, hydrological, and geological resources providing services and recreation to a large number of people. The watershed provides space and resources for a dynamic metropolitan area, the Houston- State of the Bay Galveston metroplex. It is important to understand this estuarine system for the betterment of the – 2 population that uses it and the conservation of nature that it represents. Five ecological concepts are important for understanding the physical and biological systems that operate in this space: watershed, estuary, ecosystem, food web, habitat and . CHAPTER 1 Galveston Bay and Its Environs as a Watershed Galveston Bay and the land around it fit the concept of a watershed. A watershed is the area of land that drains into a water body. In the case of Galveston Bay, the watershed comprises all of the watersheds of the tributaries—the Trinity River, the San Jacinto River and all of the creeks and bayous that feed into the rivers or directly into the bay, plus a small area of adjacent land that drains directly into the bay. All of the changes that humans make to the land surface and the stormwater drainage system alter the dynamics of water flow through the Galveston Bay watershed. So much land is covered by buildings and roads that it is much less likely for a raindrop to soak into the ground now than 100 years ago. It is likely that the water moving to the bay will carry dissolved or suspended pollutants or debris. Small tributaries to the bay now tend to have more highly variable flows because there are fewer acres of wetlands to hold and slowly release stormwater. Many areas have drainage Figure 2.2. In a watershed, the movement of water ditches or channelized bayous that are designed defines the boundaries and hydrological processes to move water quickly to the bay. connecting the atmosphere, surface and subsurface. Image source: (AWAG 2009). In contrast, the major river tributaries have been dammed as water supplies and have more uniform flows than in the past. The San Jacinto River has 2 major reservoirs: Lake Houston resulted from a dam across the East San Jacinto River in 1953; Lake Conroe, on the West San Jacinto River, was completed in 1973. The Trinity River has several reservoirs along its length, but the most important for the dynamics of Galveston Bay is Lake Livingston- the one farthest downstream, completed in 1969. These reservoirs change the dynamics of runoff and inflow in the Galveston Bay watershed. The network of smaller water bodies has also been altered in the Galveston Bay watershed over the last century (see Chapter 3). Travel across the prairie was very difficult in the 19th century. Agriculture was also challenging due to the periodic wetland nature of much of the land. The solution of developers and State of the Bay – agriculturists was to dig drainage channels, which still exist, and produce much more rapid runoff than the natural landscape. The Harris County Flood Control District estimates that about 800 miles of natural 2 drainage channels existed in the county before human modification (HCFCD 2009). At the present time there are more than 2,500 miles of channel in Harris County’s drainage system. CHAPTER 2 Watersheds in the Galveston Bay system take many shapes and sizes, with smaller watersheds nested within larger ones. Residential, industrial and agricultural lands all reside within these watersheds. Land-based activities often diminish the quality of water within the watershed. Fertilizers and pesticides from lawns, herbicides from fields, and oil and grease from roads and parking lots can progress from the land into the water when transported via surface runoff. In recent years, water management strategies have begun to follow a watershed approach to address these nonpoint sources of water pollution. Characterization of the Watershed Streams and rivers are longitudinal systems surrounded by watersheds. The Trinity River is a large river system with a watershed that extends north to encompass the Dallas–Fort Worth region. The San Jacinto River is much smaller and confined to Southeast Texas. Galveston Bay is also fed by coastal streams and bayous such as Cedar Bayou, Dickinson Bayou, and Chocolate Bayou. Watersheds play a critical role as contributors of pulses of nutrients, organic matter and contaminants to the estuary. Our current understanding indicates that freshwater inflows transport more than 80 percent of the imported carbon and nitrogen and 95 percent of the phosphorus to Figure 2.3. Map depicting the entire Galveston Bay Watershed extending from the Gulf of Mexico to the Dallas–Fort Worth Galveston Bay, with the metroplex. The Lower Galveston Bay Watershed is in dark orange. State of the Bay remainder contributed by Image source: Houston Advanced Research Center. – 2 peripheral marshes and air deposition (Armstrong et al. 1982; Borey et al. 1983; Byun et al. 2008). Also among the inputs are pollutants and debris. CHAPTER 3 The tributaries are not simply conduits for freshwater, nutrients, and sediment. They also contain dynamic ecological systems that process the materials. Without the inflow of freshwater, nutrients, and sediments transported by rivers and streams, the estuary would not exist. It would be a lagoon, a salty extension of the Gulf. The Galveston Bay watershed is defined by the watersheds of the tributaries that flow into the bay, especially the Trinity River, and the land areas from which stormwater flows directly into the bay. This book is focused on the orange-shaded portion of Figure 2.3, referred to as the Lower Galveston Bay watershed, which excludes the areas on the Trinity River above Lake Livingston dam and on the San Jacinto River above Lake Houston dam. The entire Galveston Bay watershed consists of approximately 24,000 square miles of land and water, which dwarfs the 600 square miles covered by the bay (see Figure 2.3). Within this large system, there is variation in the hydrological pattern of the various tributaries. The characteristic flow regimes of the bayous, streams and rivers are quite different. The Trinity and San Jacinto Rivers are gauged for quantity of water carried to the bay. According to the Texas Water Development Board, on average the Trinity River contributes approximately 54 percent Figure 2.4. The Galveston Bay estuary has a salinity gradient. Freshwater enters in the upper estuary and mixes with salt water from of annual freshwater inflow the Gulf of Mexico. to Galveston Bay (Powell et al. 1997; Buzan et al. 2009). Much less is known about the hydrology of bayous, the most common type of tributary to Galveston Bay. Bayous operate primarily as extensions of the tidal bay system and may have no natural source of freshwater beyond precipitation. All of the tributary types are monitored for water quality, which is discussed in Chapter 6. State of the Bay The Upper Watershed – Galveston Bay has 2 large “upper watersheds,” with a combined area of nearly 20,000 square miles 2 upstream of Lake Houston on the San Jacinto River and Lake Livingston on the Trinity River. The Trinity River extends past the Dallas– Fort Worth metropolitan area and has numerous artificial reservoirs on its CHAPTER 4 tributaries and on the main stem. Land use and land cover classes within the watershed include forest and wetland along the river floodplain, agriculture in many parts of the watershed, and urban areas and rangeland in the far northwestern part of the drainage area. The San Jacinto River is mostly forested upstream of Lake Houston, with some urbanization in its lower drainage area. Lake Conroe is a large reservoir located on the upper portion of the Western Fork of the San Jacinto River. The Lower Watershed The lower watershed is defined as the area, exceeding 4,000 square miles, draining to the bay downstream of 2 major impoundments: Lake Houston on the San Jacinto River, and Lake Livingston on the Trinity River. The 2 reservoirs attenuate some runoff and pollutant loads from the upper watershed. Therefore, the lower watershed, below the reservoirs, more directly contributes runoff and runoff-born detritus and pollutants to the bay than does the upper watershed. The metropolis of Houston and its associated suburban communities occupy the western side of the bay, while the eastern side remains largely agricultural and undeveloped. Urban and suburban development is very significant to the bay through the contribution of polluted stormwater runoff from parking lots, streets, highways, roofs, and yards (Newell et al. 1992; Basnyat et al. 1999; Wu et al. 2008). Agriculture on the eastern shore contributes nonpoint sources of herbicides and pesticides. Livestock operations can serve as sources of bacteria. Nutrients may come from a variety of sources, including agriculture, suburban development, and atmospheric deposition. As seen in Figure 2.4, Galveston Bay is commonly divided into 5 major sub-bays. The main body of Galveston Bay is broken into Upper and Lower portions.

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