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Trend estimation for complex survey designs of water chemistry indicators from Sierra Nevada Lakes.

ABSTRACT: Surveys for long-term monitoring programs managing natural resources often incorporate sampling design complexity. However, design weights are often ignored in trend models of data from complex sampling designs. Generalized random tessellation stratified samples of a simulated population of lakes are selected with various levels of survey design complexity, and three trend approaches are compared. We compare an unweighted trend model, linear regression models of the trend in design-based estimates of annual status, and a probability-weighted iterative generalized least squares (PWIGLS) approach with a linearization variance. The bias and confidence interval coverage of the trend estimate and the size and power of the trend test are used to evaluate weighted and unweighted approaches. We find that the unweighted approach often outperforms the other trend approaches by providing high power for trend detection and nominal confidence interval coverage of the true trend regression parameter. We also find that variance composition and revisit design structure affect the performance of the PWIGLS estimator. When a subpopulation exhibiting an extreme trend is sampled disproportionately to its occurrence in the population, the unweighted approach may produce biased estimates of trend with poor confidence interval coverage. We recommend considering variance composition and potential subpopulation trends when selecting sampling designs and trend analysis approaches.

SUBMITTER: Starcevich LAH

PROVIDER: S-EPMC6153522 | biostudies-literature | 2018 Sep

REPOSITORIES: biostudies-literature

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Trend estimation for complex survey designs of water chemistry indicators from Sierra Nevada Lakes.

Starcevich L A H LAH McDonald T T Chung-MacCoubrey A A Heard A A Nesmith J J Philippi T T

Environmental monitoring and assessment 20180919 10

Surveys for long-term monitoring programs managing natural resources often incorporate sampling design complexity. However, design weights are often ignored in trend models of data from complex sampling designs. Generalized random tessellation stratified samples of a simulated population of lakes are selected with various levels of survey design complexity, and three trend approaches are compared. We compare an unweighted trend model, linear regression models of the trend in design-based estimat ...[more]

PMID: 30232629

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Project description:This dataset was obtained over repeated field-trips to the Sierra Nevada Massif and contains the physical parameters of its recognised water-bodies. It therefore defines the general cartography of the area, with data on individual features regarding the geographical coordinates (x, y, z), dimensions (length, width, depth), flooded surface area, stored water volume, shoreline length, as well as the area of associated green fringes and the length of their borders. These data were basically obtained using straightforward techniques, such as GPS, tape measurements and photographic interpretation. The data were then previously used to define the role of these water-bodies in the hydrology of the massif: relationships between number of water-bodies and water volumes between 2700 and 3200 m a.s.l. regarding watersheds (Mediterranean, Atlantic and total massif), relationships with green fringes, moment of maximum snowmelt discharge and the estimation of different components of water volumes discharged during the main period of thaw. The formation patterns of each water-body were also identified in their situational context, and the role played by each formation process on the stored water volume: the water-bodies close to the peak line (2918 m mean altitude) are highly dependant on the glacial processes that created the hollows in which they are located. Slope instability created water-bodies mainly located at lower altitudes and are more fragile due intense slope dynamics. In any case, these hydrological data show a paradoxical behaviour because despite its higher xericity, the Mediterranean watershed generally has higher water contents than the Atlantic. The cause of this hydrological imbalance between watersheds seems to be unrelated to the formation processes of the existing water-bodies. Sierra Nevada is considered to be clearly representative of a high mountain Mediterranean environment, where the data collected are a starting point to define the different habitats or for investigation of the hydrological processes of the massif and their evolution. Lack of such data is often a problem that in the present case is solved with this contribution.

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Dataset Information

Trend estimation for complex survey designs of water chemistry indicators from Sierra Nevada Lakes.

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Trend estimation for complex survey designs of water chemistry indicators from Sierra Nevada Lakes.

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