Assessment of sediment phosphorus release at Uiam lake, Chuncheon

Arif Reza, Bomchul KimDepartment of Environmental Science, Kangwon National University, Korea

Abstract

Phosphorus (P) is regarded as the most critical limiting macronutrient for the growth of phytoplankton. P release from the sediments is one of the most important factors that affect the P concentration in lake water and may cause eutrophication even though the external nutrient sources are under control. So, this study focuses on assessment of sediment Phosphorus release at Uiam lake under different conditions responsible for releasing P from lake sediments.Keywords: Uiam lake, Sediment, Phosphorus, Release rate, Incubation

1. Introduction

Phosphorus (P) is regarded as the most common limiting macronutrient for the growth of primary producers (Wetzel, 2001). The water quality of lakes, streams and estuaries has been adversely affected by excessive algal growth. P release from the sediments is one of the most important factors that affect the P concentration in lake water and may cause eutrophication even though the external nutrient sources are under control (Abrams and Jarrell, 1995; Xie et al., 2003).

Sediment plays an important role in P cycling as it has the ability to accumulate a large portion of P, settle out from the water body either transitory or persistently. Transitory stored P will recycle to the water column. Under certain condition the areas where the external input of P has been evidential and transitory accumulation is significant, the recycle process can contribute more than the external input (Ahlgren et al., 2006).

The release of P from sediments has been inspected for last few decades (Nürnberg, 1987; Andersen & Jensen, 1992; Gardner et al, 2001). Due to the complicated nature of Nitrogen (N) conversion in lake sediments P input from lake sediments has drawn more attention than N (Smith, 1979). Several environmental factors like temperature, Dissolved Oxygen (DO) concentration, pH and redox potential control the release rate of P from sediments (Jensen & Andersen, 1992). Sediment P release also regulate by the total P concentration of sediments (TPS) and the relative concentration of different P fractions (Boström et al., 1988; Nürnberg, 1988).

Especially in Korea, P is regarded as the only limiting nutrient responsible for eutrophication. For implementing effective water quality management plan it is very important to control the P. This study therefore aimed to assess the P release rate from the lake sediments.

2. Materials and Methods

2.1 Study Site Description

Lake Uiam is located in Chuncheon city, Gangwon province. It was established in November 1967, the dam at Uiam Lake is located at the point where the North Han river and Soyang rivers meet. It was created to balance the flow of water to the Han River from lake Soyang and lake Paro. The hydraulic and hydrological characteristics of Uiam lake are as follows:

Table 1. The hydraulic and hydrological characteristics of Uiam lake

Watershed area (km2)

Surface area(km2)

Mean depth(m)

Residence time (day-1)

Total Volume(x 106m3)

209 15 5 6 80

2.2 Sample Collection and Treatment

Three sampling sites were selected in the lake Uiam (Figure 1). From each site, one sediment core and 2 L of overlying water were collected in September 2013 and immediately transported

to the laboratory. Upon arrival of the samples to the laboratory the samples were wrapped with aluminum (Al) foil to avoid exposure of light and stored in the refrigerator at 4oc. For release rate experiments the overlying water was siphoned off and carefully replaced with the collected filtered (Whatman GF/C) site water.

Figure 1: Sampling site (Google Earth)

2.3 Core Incubation Method

Sediment cores containing filtered water were kept in the dark at room temperature and aerated continuously with an air pump to maintain aerobic condition for 18 days. Over the incubation period 30 ml of water samples were collected regularly at 1-2 days intervals, and filtered through Whatman filter paper #42 and analyzed for Soluble Reactive Phosphorus (SRP). The amount of water removed for these samples was replaced by filtered lake water of known composition. P release rate across the sediment-water interface was the calculated as the slope of the regression line of cumulative P concentration in the overlying water against incubation time, divided by the surface area of the sediment core.

2.4 Sample analysis

Phosphate (PO43-) concentrations in the supernatants and water samples were analyzed by Ascorbic Acid method (Murphy and Riley, 1962). Sample solutions were mixed with aluminum molybdate, antimonyl potassium tartrate and ascorbic acid in an acid medium (sulfuric acid) and the absorbance of the phosphomolybdenum blue complex was measure colorimetrically at 880 nm after 15-60 minutes using a UV-Vis spectrophotometer (Shimadzu UV-1700).

3. Results and Discussion

Sediment Phosphorus release

A positive mean P release rate of 1.987±0.062 was obtained in the lake Uiam sediment cores over the 18 day aerobic incubation (Table 2), which was an indication of a net P release from sediments into the overlying water column. On the whole, the P release from the lake Uiam sediments values was comparable to values of 1.03 and 2.71 mgm-2d-1 reported, respectively for the lake Eucha ( Haggard et al., 2004) and the lake Apopka (Moore et al., 1991). Results obtain from this study indicate that lake Uiam sediments would likely be a P source under ambient P concentrations.

Table 2: Phosphorus release from lake Uiam sediments under aerobic condition

Site Phosphorus release (mgm-2d-1)S-1 (STP) 3.91±0.046

S-3 (Gongjichon) .064±0.078Average 1.987±0.062

Figure 2: Schematic diagram of the experiment (aerobic)

4. Future works

My future plan of work includes assessment of P release from sediments under anaerobic condition, investigate the effect of pH on P release, evaluate temporal and spatial variability of sediment P input, determination of total P concentration of sediments (TPS) and the relative concentration of different P fractions in sediments, characterization of P sorption and determining the best approach and appropriate dosage of chemical amendments for reducing sediment P release.

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Figure 3: SRP concentrations under aerobic conditions with incubation time in the overlying water of the intact sediment cores from site-1 in Uiam Lake

Figure 4: SRP concentrations under aerobic conditions with incubation time in the overlying water of the intact sediment cores from site-3 in Uiam Lake

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