Diurnal Fluctuations in a Pond

Introduction

Large amounts of diurnal fluctuations in factors like dissolved oxygen, pH, carbon dioxide and temperature are experienced by eutrophic ponds. As a result, the water quality is also constantly changing. The survival of animals like the fish that live in the pond is heavily depended upon their adapting capacity to the fluctuations. Any drastic changes in the quality can lead to ill effects in supporting the floral and faunal population in and around a pond. Thus it is important to monitor the quality parameters of a pond that supports some wildlife.

Data for the diurnal changes in the chemical and physical components of ponds has been collected for decades now. The first of such a kind in DO measurements was conducted by Morren & Morren in 1841. Some amount of work has also been conducted by Birge & Juday in 1911 and Scott (1924). Philip (1927) , and Czezegy (1938) have also conducted some experiments comparing the pH variations. However, majority of this work has been conducted in lakes and little data exists observing the fluctuations in ponds.

In an effort to understand the physio-chemical changes in a pond over a 24 hour period, this study was conducted in which the DO and temperature changes were recorded over a 24 hour cycle. This paper describes the dynamics of the San Joaquin Wildlife Sanctuary set in Irvine, CA. The reserve consists of a number of wetland habitats, which includes a number of shallow ponds.

The Diel oxygen Change method was adopted for recording the change in Oxygen concentration over 24 hours. The method helps average the entire community's metabolism and not just the planktons. Oxygen is known to enter the pond through photosynthetic production by plants or through atmospheric diffusion. It is also known that oxygen is poorly dissolved in water and is around 7.84 mg/L as compared to 150 mg/L in air (Ibanez, Hernandez-Esparza et al. 2008) . Since ponds lack in aeration, it is predicted that photosynthesis is the major source of dissolved oxygen. Such ponds must exhibit diurnal changes in DO concentration since the rate of photosynthesis for plants varies over 24 hours. The balance between respiration and oxygen production is focused upon in this study. It is predicted that the production over respiration ratio will be higher during day time since plants are producing oxygen and will fall at sunset and sunrise when respiration exceeds oxygen production(Wetzel 1975). This leads us to examine whether the ponds are predominantly autotrophic or heterotrophic. Autotrophic ponds are characterized by a community where oxygen productivity is higher than respiration and a heterotrophic one is where respiration exceeds oxygen production (Wetzel 1975). Our study will also compare the DO concentrations between the top and the bottom of the pond waters. Based on the fact that the surface is more exposed to the air, the surface waters