A Review of lake vertical profile monitoring in the Southwest Alaska Network: Recommendations for future efforts

Wilson, Tammy; Moore, Claudette

The Southwest Alaska Inventory and Monitoring Network monitors freshwater systems in five national park units: Alagnak Wild River (ALAG), Aniakchak National Monument and Preserve (ANIA), Katmai National Park and Preserve (KATM), Kenai Fjords National Park (KEFJ), and Lake Clark National Park and Preserve (LACL). To date, most of our efforts have focused on field testing and modifying protocols for water quality and hydrology monitoring on high priority lake systems. In this report we evaluate two aspects of water quality sampling collected from vertical profiles in Lake Clark National Park and Preserve. First we evaluated the ability of field sampling methods to produce precise measurements, and then we evaluated the efficiency of the sampling design for smaller lakes. Water quality sampling was initiated in Lake Clark in 2008 and expanded to other lakes in the subsequent years. Sampling was conducted at ten sample sites in each lake basin (there are three basins in Lake Clark, and one in smaller lakes) using a multiparameter instrument (sonde) to record four water quality parameters (temperature, pH, dissolved oxygen, and specific conductivity). Sampling is conducted at 18 depth categories along the thermal gradient to a maximum depth of 50m. This method created ten vertical profiles of each parameter for each lake basin. Parameter measurements were recorded twice at each depth class, once when the sonde was descending, and again when it was ascending. We used repeated measurements collected from each sample location in Lake Clark to evaluate measurement precision, and found statistically significant differences between repeated measurements; especially in measurements of pH. These differences were likely due to in situ equilibration protocols, and resampling procedure. We suggested changes to field protocols that will improve the quality of data obtained from lake sampling. We then evaluated the necessity of sampling all lakes with a minimum of 10 spatial replicates. We found that in small lakes with homogeneous basins, water quality estimates were well represented by a single measurement collected from near the center of the lake. Based on this outcome, we suggest using mid-lake sampling for small lakes with uniform lake basins. These changes will enable SWAN staff to improve data quality, and increase the sampling frequency for tier 2 lakes.

A Review of lake vertical profile monitoring in the Southwest Alaska Network: Recommendations for future efforts

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