Water 2013, 5, 988-1005; doi:10.3390/w5030988 OPEN ACCESS water ISSN 2073-4441 www.mdpi.com/journal/water Article Past, Present, and Future Nutrient Quality of a Small Southeastern River: A Pre-Dam Assessment Jonathan M. Miller and Paul M. Stewart * Department of Biological and Environmental Sciences, Troy University, Troy, AL 36082, USA; E-Mail: jmiller7557@troy.edu * Author to whom correspondence should be addressed; E-Mail: mstewart@troy.edu; Tel.: +1-334-670-3932; Fax: +1-334-670-3662. Received: 21 April 2013; in revised form: 14 June 2013 / Accepted: 27 June 2013 / Published: 8 July 2013 Abstract: Riverine dams alter both the physical environment and water chemistry, thus affecting species assemblages within these environments. In the United States, dam construction is on the decline and there is a growing trend for dam removal. The Choctawhatchee, Pea, and Yellow Rivers Watershed Management Authority had initiated the permitting process for placing a reservoir dam on the Little Choctawhatchee River (LCR), a tributary to the Choctawhatchee River. The purpose of the proposed reservoir was water supply, and while the permit application has been suspended, history shows that this or related projects are likely to arise in the future. This study collected data on nutrient quality seasonally (four times) from 12 sites in the LCR watershed from October 2007 to June 2008 in order to determine pre-dam conditions and to compare these data to historical and regional information. Historical and current nutrient concentrations were elevated throughout the watershed, in most cases above suggested criteria, and indicated that water quality of the river was and continues to be nutrient rich. A future reservoir at recent levels of water quality will likely be highly eutrophic, and anthropogenic influences will further stress this ecosystem and its water quality as the urban region expands. Keywords: Choctawhatchee; Little Choctawhatchee River; water quality; reservoir; dam; nutrients; wastewater; phosphorus; nitrogen Water 2013, 5 989 1. Introduction The environmental effect of dams on riverine systems includes the degradation of habitat and river morphology [1,2] and the decline of water quality [3,4]. The number of dams being built across the United States began decreasing after the 1960s [5]. Of the 1995 dams reported in the National Inventory of Dams (NID) for Alabama, the number of dams being built has decreased in Alabama since the 1960s, with the majority of dams built being low-hazard earth dams [5] which are typically small scale farm ponds. Riverine impoundments often impact water chemistry by increasing concentrations of nutrients [6], and decreasing levels of dissolved oxygen. Reservoirs not only increase certain chemical concentrations to harmful levels, but also reduce needed parameters to critical levels by acting as annual sinks for organic and inorganic compounds [7]. Even though a reservoir may act as a flow-through system, dams often act as large nutrient traps that slow nutrient advancement [3]. Concentrations and ratios of nutrients play a critical role in eutrophication and the development of algal blooms [8], which can be toxic to humans and animals and are often a nuisance. When nuisance algal blooms die, these can deplete the reservoir of oxygen leading to fish kills, noxious odors, and other problems associated with decaying organic matter. In addition, regional variations play a vital role in the processing of retained nutrients in reservoirs [9]. The Choctawhatchee, Pea, and Yellow Rivers Watershed Management Authority (CPYRWMA) had initiated the permitting processes for the placement of a reservoir dam on the Little Choctawhatchee River (LCR) for a drinking water supply, though the recent permit has been suspended. The need for baseline nutrient information is important when little historic data are available, so that the future nutrient status of the reservoir can be predicted. This study focused on the nutrient quality of the LCR and its tributaries. The objectives were to: (1) describe the nutrient conditions of the river over a one-year period; (2) compare nutrient data with historical and regional measurements and to nutrient criteria; and (3) discuss future water quality of a proposed reservoir, if built. 2. Materials and Methods 2.1. Study Area The LCR is a tributary to the Choctawhatchee River located in southeastern Alabama, USA (Figure 1). The LCR system drains the northern and western sides of Dothan, AL and primarily borders the Dale and Houston County line. The watershed covers about 430 km2 and is comprised of low-gradient streams with sand and marl bottoms. Urban development and agriculture are currently the dominate land uses within this area. Conversion of forested habitats for urbanization and agricultural purposes has caused numerous changes in stream habitats including destabilization of stream banks, increased sedimentation from eroding fields and developing areas, chemical changes from fertilizers and biocides, and alteration of light, thermal regimes, and hydrologic conditions [10]. The dam’s intended location was upstream of an old power dam at Dale County Road 121, and is between Highway 123 and County Road 9 on the border of the Dale and Houston County line, near Panther and Bear Creeks [11]. The proposed reservoir of the LCR would have had a normal pool depth of 9.75 m and a normal pool area of 592 ha [11]. Water 2013, 5 990 Figure 1. Little Choctawhatchee River near Dothan in southeast Alabama. 2.2. Nutrient Sample Collection and Analysis Twelve sites were selected within the LCR watershed (six sites on the Little Choctawhatchee River and six sites on tributaries) (Figure 2). Using standard sampling protocols [12], nutrient variables were measured seasonally (four times) at each site to provide baseline nutrient data for the watershed. Nutrients measured included total phosphorus (TP), orthophosphate (OP), and nitrate (NO2 + NO3). All grab samples for laboratory analysis were collected at approximately 15 cm depth, in flowing water where available, in acid-washed (10% HCl) 125 mL Nalgene® narrow-mouth HDPE bottles, transported on ice to the laboratory, and analyzed within appropriate time frames [12]. Grab samples were taken in separate containers for TP (unfiltered), and OP and NO3 (filtered, 0.45 µm). Duplicate water samples were collected for >10% of the samples for quality control. The Hach DR/2800 (Hach Company, Loveland, CO, USA) was used to measure all nutrient concentrations. All means (in our study and others referenced) were calculated from grab samples, therefore not implementing discharge to determine mean loading. Measurements under the detection limit were calculated as one half the detection limit in computing means. Total phosphorus (TP) was measured with Hach Method 8190 (Hach Company) using program 3036, with detection limits ranging from 0.02 to 1.14 mg/L P [13]. Orthophosphate (OP) concentrations were measured with Hach program 3025 PhosVer3 (Ascorbic Acid) Method 8048, with detection limits from 0.01 to 0.81 mg/L P [14]. Nitrate (NO3) was measured using procedure 8192 [15], with detection limits ranging from 0.01 to 0.50 mg/L NO3-N. This method converts nitrite (NO2) to nitrate (NO3), and actually measures NO2 + NO3 as N. All values found to be above detection limits were derived by diluting samples with deionized water prior to analysis [12]. 2.3. Data Analysis Box plots were used to visually compare nutrients over the entire year (four samplings) by site. Nutrient information gathered in the present study was compared to past nutrient data of the LCR found in the Water 2013, 5 991 literature, regional data, U.S. Environmental Protection Agency (EPA) regional criteria [16], phosphorus levels considered to be eutrophic by Dodds et al. [17], and nitrogen levels indicative of excessive algae growth [18]. Figure 2. The Little Choctawhatchee River watershed demonstrating general land use and the twelve stream sampling sites near Dothan in southeast Alabama, USA. 3. Results 3.1. Recent and Seasonal Condition of the LCR Watershed Total phosphorus (TP) varied from below detection limits (
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