4. Discussion
4.1 Temporal and Spatial Differences in Water Quality
Since I did not do a regression or correlation analysis I can not state that there is a causal relationship between land use and water quality; temperature, dissolved oxygen, and conductivity. I can, however, make general comments about these variables relationship to specific land use and any trends noticed between spring and summer sampling periods. Water temperature was higher during the summer sampling period, and the lower water temperatures observed in forested reaches during both sampling periods and the relatively high levels found at industrial and agricultural sites in summer is likely due to lack of riparian shade in agricultural and industrial areas (figures 2 and 3).
One of the most important parameters of water quality, to aquatic life, is oxygen. Fish respire by passing water containing dissolved oxygen, over their gills. The oxygen enters the water through contact with the atmosphere or from photosynthetic activity of aquatic macrophytes and algae. Dissolved oxygen concentration in the water is a result of the balance of oxygen entry and oxygen consumption, usually by organisms. Hypoxia occurs in aquatic environments when levels of dissolved oxygen become reduced to a point where it is detrimental to organisms, and anoxia is a complete lack of dissolved oxygen. A healthy DO level is around 80% saturation and 8mg/L at 19oC (Davis 1975). The minimum requirement for fish growth and activity is 4-5mg/L for most species and the point at which an animal would suffocate is species dependent, but is typically below 2 mg/L or 30% (Diaz 2001). Severe hypoxia or anoxia will result in a fish kill if they are unable to escape. In this study dissolved oxygen ranged from very low hypoxic-anoxic levels, below 1mg/L, to supersaturated conditions, above 12mg/L (figures 2 and 3). Dissolved oxygen levels, were generally lower in summer (figure 3), likely due to warmer water temperatures, the depressed oxygen solubility of warmer water, and reduced flow (Hall & Schreier, 1996). This was most evident at agricultural sites, which had significantly lower dissolved oxygen levels and warmer temperatures than other sites during summer, which could be attributed to the lack of riparian or shade vegetation in those areas along Bertrand Creek. Most forest sites maintained fairly good levels of dissolved oxygen through spring and summer, which may be due to having lower water temperatures due to a forested riparian area and the influx of cool groundwater sources in Pepin Creek.
During the spring all land use types had conductivity levels below 300uS (figure 4). Summer conductivity was extremely higher at sites with an increased level of agriculture and slightly higher in urbanized areas, however there is a large standard deviation for both land uses (figure 4). The high levels could be due to higher levels of nitrate and nitrite and phosphate, which are typically associated with these land use types (Baker, 2003).
Since I did not do a regression or correlation analysis I can not state that there is a causal relationship between land use and water quality; temperature, dissolved oxygen, and conductivity. I can, however, make general comments about these variables relationship to specific land use and any trends noticed between spring and summer sampling periods. Water temperature was higher during the summer sampling period, and the lower water temperatures observed in forested reaches during both sampling periods and the relatively high levels found at industrial and agricultural sites in summer is likely due to lack of riparian shade in agricultural and industrial areas (figures 2 and 3).
One of the most important parameters of water quality, to aquatic life, is oxygen. Fish respire by passing water containing dissolved oxygen, over their gills. The oxygen enters the water through contact with the atmosphere or from photosynthetic activity of aquatic macrophytes and algae. Dissolved oxygen concentration in the water is a result of the balance of oxygen entry and oxygen consumption, usually by organisms. Hypoxia occurs in aquatic environments when levels of dissolved oxygen become reduced to a point where it is detrimental to organisms, and anoxia is a complete lack of dissolved oxygen. A healthy DO level is around 80% saturation and 8mg/L at 19oC (Davis 1975). The minimum requirement for fish growth and activity is 4-5mg/L for most species and the point at which an animal would suffocate is species dependent, but is typically below 2 mg/L or 30% (Diaz 2001). Severe hypoxia or anoxia will result in a fish kill if they are unable to escape. In this study dissolved oxygen ranged from very low hypoxic-anoxic levels, below 1mg/L, to supersaturated conditions, above 12mg/L (figures 2 and 3). Dissolved oxygen levels, were generally lower in summer (figure 3), likely due to warmer water temperatures, the depressed oxygen solubility of warmer water, and reduced flow (Hall & Schreier, 1996). This was most evident at agricultural sites, which had significantly lower dissolved oxygen levels and warmer temperatures than other sites during summer, which could be attributed to the lack of riparian or shade vegetation in those areas along Bertrand Creek. Most forest sites maintained fairly good levels of dissolved oxygen through spring and summer, which may be due to having lower water temperatures due to a forested riparian area and the influx of cool groundwater sources in Pepin Creek.
During the spring all land use types had conductivity levels below 300uS (figure 4). Summer conductivity was extremely higher at sites with an increased level of agriculture and slightly higher in urbanized areas, however there is a large standard deviation for both land uses (figure 4). The high levels could be due to higher levels of nitrate and nitrite and phosphate, which are typically associated with these land use types (Baker, 2003).