Spatial gradients in wetland water chemistry attributes across a landscape gradient of permanent and ephemeral wetlands

Background/Question/Methods

The Chippewa Moraine of Wisconsin is a diverse glacial landscape with thousands of forested ephemeral and permanent wetlands. The spatial gradient of the environmental attributes in these wetlands could provide better understanding of the preferred conditions of some macro-invertebrate and plant communities, and their abilities to disperse to sites with those conditions. Ephemeral ponds dominate the southwestern area of our study while ephemeral ponds are interspersed with permanent wetlands and larger lakes in the northeastern area. The objective of our study was to determine how wetland attributes changed along the spatial gradient, and whether the importance of space differed between permanent and ephemeral wetlands. We examined the relationship between spatial variables and water chemistry attributes, including pH, specific conductivity, temperature, dissolved oxygen, nitrates, ammonium, and phosphorus in 56 permanent and ephemeral wetlands across this 4.5 km long SE-NW gradient.

Results/Conclusions

pH was significantly correlated to longitude and latitude in ephemeral ponds (y = -5.3*longitude + 20.82*latitude  - 1419.7, R² = 0.317, F_{2, 37} = 4.88, P < 0.001). pH was was positively related to latitude in permanent wetlands (y = 38.66x - 1741.6, R² = 0.420, F_1,14= 9.40, P = 0.009).  Conductivity was significantly negatively related to latitude in permanent wetlands (y = -693.9x + 31398, R²= 0.319, F_1,13= 6.10, P = 0.028). There was not a significant relationship between conductivity and geographic setting in ephemeral wetlands. Nitrate concentration was significantly higher in northern latitude ephemeral wetlands (y= 207.97x – 9393.3, R² = 0.131, F_1,39= 5.71, P = 0.022) while water temperature was significantly lower (y=-95.086x +4310.6, R² = 0.167, F_1,27= 5.22, P = 0.031). The possible mechanisms leading to these differences include increased interaction with groundwater contribution due to more permanent wetlands in the northeast, potentially larger watersheds in the hilly topography of the northern latitudes, and deeper ephemeral ponds.