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Assessing the Condition of New Zealand's Shallow Coastal Lakes

Scope:

We are developing a model with which the "ecological integrity" (EI) of shallow coastal lakes in New Zealand can be estimated from a set of basic measurements/observations. Our goal is to provide objective and defensible assessment of shallow coastal lakes for conservation planning and prioritization.

For an overview of the while project please refer to the related forum: http://wai.yuku.com/topic...ial-river-indicators.html

We are now testing the usefulness of approximately 50 chemical, biological and physical metrics from a set of 45 representative New Zealand lakes as predictors of EI. We are using human pressure gradients developed by the Department of Conservation (Water Bodies of National Importance or WoNI indicators) as proxies for EI. Pressure gradients most likely to be associated with lake EI and condition are: catchment impervious area (%), native vegetation removed from the catchment (%), and both N and P loads adjusted for water residence time in lakes.

There are a number of challenges we face in developing a useful model:

1) Very few historical data on shallow coastal lakes are available. Our data collections for each lake, although labour intensive, still represent just one point in time in dynamic systems.

2) No established integrity-related metric, such as the MCI used in streams, is available for lake ecosystems.

3) We lack reference sites - especially in intensively agricultural regions such as Canterbury. As a result most lakes in the best condition (probable highest integrity) included in our study were on the West Coast of the South Island. Effects of region will be difficult to separate from disturbance.

These limitations, however, are fundamental tradeoffs that most managers face. Effective management will require that we learn how to work with these limitations and make the best assessments with the information available to us.

Request for Your Feedback:

We would like your comments and suggestions regarding the shallow lake EI approach from the perspective of a potential end user. Table 1 summarizes the 10 most promising metrics (those with the best relationships to the WoNI pressure gradients) according to our preliminary boosted regression tree and correlation analyses. The eventual EI model will be based upon a multiple, curvilinear regression calculation that will require at least two measured indictors (inputs from field assessments/measurements).

Questions:

Assessment would require collection of between 2 and 10 of the metrics listed.

1) Do the metrics listed below fit into existing monitoring efforts?

2) Are any of the indicators out of the question, and if so why?

3) Are the WoNI pressure gradients listed above reasonable proxies for integrity? Are there better, quantitative, widely-available alternatives?

4) Do you believe that "expert opinion" is a useful, defensible assessment? How could it be improved or made more objective?

Note on Expert Opinions

"Expert Opinion" was derived by averaging independent rankings made by three professionals who have worked in the field of aquatic ecology for at least 15 years. There was ~80% agreement between the experts for our set of 45 lakes. Expert opinion was closely correlated with the % native vegetation removal pressure index (r² = 63%), but only very weakly with impervious area and N or P loading.

Expert opinion, while in some ways subjective, integrates years of experience and specialized knowledge of water chemistry, longer-term biological processes and landscape characteristics (e.g. this lake overlies a limestone formation, so a high pH in this case does not indicate eutrophy). It also includes a greater understanding of the context natural variability, seasonality, and many other integrated drivers and responses. We note that strict quantifications and analyses are not completely immune to subjective interpretations. Additionally, opinions of many experts can be averaged. However, opinions may be ultimately lack defensibility in formal settings such as court.