# Multidimensional Assessment of Lake Water Ecosystem Services Using Remote Sensing
## 4 Discussion  
We analyzed the lake water provisioning services in Minnesota from both spatial and temporal perspectives. The temporal analysis shows that lake water storage in Minnesota fluctuated over time from 1998 to 2018 with an increasing interference, which is consistent with the results of the Lake Hydrology Program [78]. According to Minnesota's water supply report by the Minnesota Department of Natural Resources Waters [79] and Minnesota water use report by the University of Minnesota Water Resources Center, surface water plays an essential role in water provisioning in Minnesota, such as public water supply and irrigation, and cooling in power generation. About 18.6% of the water comes from groundwater, and the remaining water used comes from surface water. They also found a growing consumption of surface water, which could contribute to the increasing disturbance we found in this study. Water provisioning output, efficiency, and trend have relatively stable spatial distribution, while the clustering patterns are different: (1) The high-value output zones are located in Northeast Minnesota, including Northeast, North Central, and East Central, dominated by forests. This distribution does not necessarily match the demand distribution for agricultural and industrial water use. We should consider the availability of abundant water provisioning for agricultural and industrial processing in the development plan. Only one high-value cluster in water provisioning output indicates that the water provisioning output is sound in total; there is no large-scale water shortage area. (2) Efficiency represents the water provisioning capacity per unit surface water ecosystem. The spatial distribution is similar to the output; high values are concentrated in Northeastern Minnesota. Thus, the spatial mismatch between supply and demand also exists in the distribution of efficiency. Unlike the output, the low-value clusters are significantly inefficient, which means the water provisioning capacity per unit of surface water is flimsy, where the below-average zones frequently appear considerably. (3) Compared with the above two indicators, the trend index distribution is largely random. However, the low-value area significantly expanded, so as the hot spots and cold spots. It shows that the water provisioning trend index declines over time, the below-average area expands, and extreme values are gathering considerably. Projections from co-ordinate planes defined by assessment dimensions prove water provisioning efficiency is positively dependent on output, where output is above-average, the efficiency is above-average, too. While output is negatively dependent on efficiency, where efficiency is below-average, the output is below-average also. These correlations should be considered in surface water resources management and ecosystem protection projects. We identified nine counties, including Becker, Cass, Clay, Douglas, Lincoln, Pope, Stevens, Transverse, and Yellow Medicine, where water provisioning service is degrading in the five studied years and fifteen counties degraded for four out of five years. Counties with severe water provisioning degradation are mainly concentrated in three zones (Northeast, East Central, and Southeast) in Western Minnesota. The degradation area distribution is consistent with the distribution of cropland in Minnesota, while it does not match the population and industry distribution. Agricultural activities have proved to be highly dependent on surface water availability [80]. Simultaneously, the human disturbances to surface water are strong where the agricultural activities are vigorous, such as dam water storage and irrigation drainage [81; 82; 83]. Thus, it is reasonable that prosperous agricultural production is primarily responsible for the degradation of water provisioning services in Western Minnesota, compared with the population or industrial activities.