GEOG 566






         Advanced spatial statistics and GIScience

May 8, 2017

Tutorial 1: Nitrate Concentration Differences: Between Sites and Over Time

Filed under: 2017,Tutorial 1 @ 10:26 am

Research Question: 

Do the differences in nitrate concentrations indicate a pattern between site locations, and do they show a pattern over time.

Tools and Approach: 

I performed the analysis largely in excel, though ARC GIS mapping software was useful in spatial proximity analysis. I was able to produce a chart and representative scatter plot of the nitrate concentration differences over time between various sites. The sites are naturally grouped/divided into three groups based on spatial location. The first is the Rock Creek basin (and the example used in this tutorial) additionally I analyzed Mary’s Peak streams and finally the Coastal streams.

Analysis:

First, I sorted my concentration data that I had produced for exercise one (Table 1). Table 1 represents total nitrate concentrations in ppm for all sites. Next I subtracted the concentration data between streams within varying proximity (Table 2). The second table represents the differences in concentration values, a negative value correlates with a higher nitrate concentration in the stream that was being subtracted. This analysis allowed me t
o find concentration of the nitrate data between points (stream sites) and over time.

Results

Rock Creek Basin:I found higher differences (indicating higher nitrate concentrations) in the mainstem rivers than the tributaries. Additionally, I saw higher concentrations of nitrate in the spring samples as compared to the winter samples. I     expected higher values for nitrate in the mainstem, such as rock creek due to the concentration of water coming from upstream. Naturally the smaller tributaries would exhibit lower concentrations than the larger order stream that catches the two. I also expected nitrate differences and concentrations to decrease in the spring time. If the inputs of nitrogen to the system remain relatively stable, then the uptake length of nitrate (the most sought after in stream nutrient cycling) would shorten and cause the concentrations of nitrate sampled to decrease.

 

 

 

 

 

 

 

 

Critique of Method:

This method was useful as it made me think about my data set in a different way. Using the differences in concentrations over time, I was able to think about two variables (Y) difference in concentration, and stream site location to assess why each site exhibited the data it did. I was able to determine that upstream site locations typically have lower concentrations of nitrate then the downstream sites. I also was able to think about how nitrate is available as the seasons change from winter to spring. At first I wasn’t able to understand why nitrate concentrations could decrease in the winter months, but a combination
of lower flows and increase macroinvertebrate activity are potential players in a decrease in concentration.

 

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