Drought Impact on Water Quality
Impact of drought on water quality is one of the research areas focused by the drinet team. Hydrological impacts of drought have been widely analyzed but the environmental impacts of droughts have received only perfunctory and qualitative attention. Quantitative analysis of the role of droughts on stream water quality has not been forthcoming probably due to the lack of availability of water quality data and the inherent process complexity.
Study Area and Data Availability
The St. Joseph River watershed(HUC # 04100003; Fig 1), with a drainage area of 2800 km2, is located in Indiana, Michigan, and Ohio. The weekily timeseries data of water quality parameters for the basin (location as in Fig 1) were available for 11 years (1998-2008) from St. Joseph River watershed initiative. The quality parameters includes Phosphorus, Ammonia, Atrazine, Cyanazine, Alachlor, Metachlor, E.Coli and Total Coliform.
The study is proposed with analyzing the indication of drought on water quality data with different severity of drought. Droughts over different durations (monthly, seasonal, 6 months and annual, Fig.2) were identified using the Standardized Streamflow Index (SSI) (Kao and Govindaraju, 2010). SSI is a probability index based on the probability of recording of streamflow, the probabilities are standardized so that an index of zero indicates median streamflow. The index is negative for drought and positive for wet period.
The water quality analysis is performed using both load and concentration of different constituents. The daily loads were estimated using LOADEST model; a regression model which requires observed constituent concentrations and daily streamflow values. However, daily data cannot be estimated for E. Coli and Total Coliform using LOADEST, so for these constituents analyses was conducted using measured data only. The preliminary analysis has been done using the Cedar Creek basin data.
- Measured data analysis indicates high concentration during wet year compared to dry year. This indicates the non point source pollution as the driving factor affecting water quality
- Correlation analysis shows a positive trend for nutrients especially loads with wetness; but load will be always directly correlated with flow. A comparison of nutrients and pesticides concentration trend shows the nutrients has a positive correlation with wetness (SSI).
- The seasonal and 6 months analysis also shows a high concentration and load during wet period than the dry period
- Results indicate that droughts exert an important control on water quality both in terms of concentrations and loads.
- The results of analysis using LOADEST simulated values are always biased with stream flow. A better understanding of the processes is possible by using watershed models such as SWAT
- Limited data availability: 11 years of weekly data is a shortfall for data driven analysis especially for hydrological events such as drought