Limitations of early PSTA research Sample Clauses

Limitations of early PSTA research. The prior PSTA investigations (not including those with the current STA-3/4 PSTA Facility) helped characterize construction challenges (the importance of elevation control during construction) and operational issues (seepage and flow quantification, types of macrophyte and periphyton) pertaining to PSTA community development. However, we identified three major shortcomings prevalent in previous PSTA research efforts: 1) durations were short, typically 12 – 27 months; 2) limerock substrates were “raw” (i.e., freshly scraped or quarried, rather than covered by mature periphyton communities and accrued sediment, and; 3) replication of treatments was poor. Short duration experiments are necessary and useful to generate new information quickly. Any full-scale PSTA implementation, however, will need to operate indefinitely for the continued protection of the Everglades. Short-term studies potentially miss two challenges of long-term operation. First, long-lived treatment wetlands inevitably face irregular, unpredictable perturbations, especially from the climate. The resilience of the PSTA technology to uncontrollable impacts (e.g. drought, hurricane, biological invasion) cannot be easily tested in short-term studies. Second, some treatment wetlands have demonstrated declining P removal performance after many years of operation (e.g. Xxxxxxx Xxxxxxxx Wetland), which may require addition management intervention. This is difficult to predict with short-term experiments. As noted previously, PSTA studies have operated on a variety of substrates, including peat, shellrock and sand (CH2M-Hill 2003, XxXxxx et al., 2004, XxXxxx et al., 2011), but most were of short duration (typically < 24 months). None of these prior investigations used “accrued” PSTA sediment; only the original inert material (i.e., the “starting substrate condition”) was utilized. A disadvantage to short-term experiments is that any initial substrate material present during establishment will be covered by accruing sediment material, which is more representative of long-term operational conditions. Hence, the long-term sustainability of the PSTA concept is ill defined. We address this through experimental work comparing newly-accrued sediment from the STA-3/4 PSTA Cell to exposed limerock substrates. Several of the early projects were conducted with little or no experimental replication. This design can be useful for less-costly pilot or range-finding studies, but the results are not reliable for de...