Investigating into the Effect of Nitrates Levels on the Invertebrate Abundances of Two Contrasting Streams

Investigating into the effect of Nitrates levels on the invertebrate abundances of two contrasting streams.

Nitrate Concentration

Natural nitrate levels in groundwater are generally low, usually less than 10 mg/l NO3, however concentrations can increase due to human activities, such as agriculture, industry, domestic effluents and emissions from combustion engines. The legal maximum concentration of nitrate for human drinking water in the uk is 50mg/l. Appendix 1 shows the causes of nitrate pollution in groundwater and Appendix 2 shows the safe nitrate levels in drinking water and its scale of toxicity.

The sources of nitrate pollution in groundwater are:

• cultivation in areas where the soil layer is relatively thin, has poor nutrient buffering capacity or where there are changes in land use;
• over fertilization of crop for intensification of agricultural activity;
• spread cultivation of crops which require high fertilizes doses and which leave the soil bare over long periods (maize, tobacco and vegetables);
• drainage systems which lead to drainage of fertilizers;
• intensive agricultural rotation cycles involving frequent ploughing and extensive areas of bare soils during winters;
• organic fertilizers form animal husbandry;
• increased urbanization.        

1) Lenntech. (2016).

Nitrate is an essential plant nutrient and a natural constituent of any soil. It is an important source of nitrogen for plant growth. However, if the soil contains more nitrate than plants can use, then the excess nitrate can be leached from the soil and contaminate groundwater.

Most nitrate leaching occurs over the winter months, when plant growth is slow, soils are wet and rainfall is plentiful. Nitrate concentrations in groundwater are highest in the winter and springtime as a result. In the summer and autumn, plants are growing and taking nitrate and water from the soil, so nitrate leaching rates are lower. As a result, nitrate concentrations in groundwater generally decrease in summer and autumn.

2) ecan.gov

Invertebrate Species

Species that are tolerant and intolerant to high nitrate levels include:

Locations

The two contrasting streams we are investigating are Settrington Beck and Brompton Beck. Settrington Beck is a minor chalk stream surrounded by chalk hills and land used for agriculture. On the other hand the land around Brompton Beck is not as heavily farmed and the limestone not as pure.[pic 12][pic 13]

Method

Sampling

Area was not homogenous and we could assess the proportions of distinct microhabitats. I sampled using the stratified sampling technique. I divided the entire population into different subgroups, then randomly selected the final subjects proportionally from the different subgroups. I could representatively sample even the smallest and most inaccessible subgroups in the population allowing me to sample the possible extremes in the given population. With this technique I had a higher statistical precision compared to simple random sampling as the variability within the subgroups is lower compared to the variations when dealing with the entire population.