Determining reference conditions for nutrients, chlorophyll a and Secchi depth in Yungui Plateau ecoregion lakes, China

Abstract

Establishing nutrient reference condition (baseline environmental condition) of lakes in ecoregion is a critical consideration in the development of scientifically defensible aquatic nutrient criteria. Three methods were applied to determine reference conditions in Yungui Plateau ecoregion lakes with respect to total phosphorus, total nitrogen, planktonic chlorophyll a (chl a) and Secchi depth. First, minimally developed lake/catchment units were identified based on existing geographical database and visual basin survey. Lakes in these catchments were considered minimally disturbed ‘reference lakes’. Second, the frequency distribution of all of the lake data presently available by each variable was plotted, and the lower 25th percentile was selected as the reference condition for each value. Third, median nutrient, chl a and Secchi depth values were determined for the best one‐third of lakes and applied as indicators of reference condition. The result of model prediction and data from historical record were used to test three techniques for determining reference condition. Reference conditions, as determined by these three methods, broadly agreed for all parameters. Overall, the data suggest that multiple methods can be used to determine reference condition, and that in Yungui lakes, reference condition corresponds to oligotrophic–mesotrophic status.

Lake ecoregions and nutrient criteria development in China

“…This finding is attributed to many factors, especially sufficient sunlight and warm temperatures (Huo et al, 2012). Moreover, the TSI (SD) was larger than the TSI (Chl a); except for algae, the SD cannot be used to indicate the use-impairment related to algal blooms in this ecoregion (Carlson and Havens, 2005), primarily because dim light also affects the Secchi transparency of this ecoregion, which is most composed of deep lakes.…”

Defining Reference Nutrient Concentrations in Southeast Eco‐Region Lakes, China

“…If one method may define an unexpectedly high or low reference condition, such a reference condition can be tested and verified by the other methods . Thus, the values and ranges considered as nutrients reference conditions for Southeast eco‐region lakes were given as follows: TP 0.020–0.025 mg/L, TN 0.55–0.65 mg/L, Chl‐a 1.6–2.50 mg/m 3 , SD 2.00–2.50 m.…”

“…This is mainly because that the other factors (except nutrients), such as climate, light intensity, and organic matter content in water would have a positive and negative effect on the growth of algae . Finally, although many studies had shown that the good correlation was existed between Chl‐a and SD , the lake depth, organic matter, dissolved color, and particulate matter would impact the value of SD . Hence, it is not necessary to have high transparency correspondingly when the Chl‐a reference concentration was low (e.g.…”

“…TN concentration obtained by extrapolation approach was much higher than that by the other methods, may because that there were no significant correlation existed between TN and Chl-a, leading to the weak constraint ability of established extrapolation model for TN. If one method may define an unexpectedly high or low reference condition, such a reference condition can be tested and verified by the other methods [12,13]. Thus, the values and ranges considered as nutrients reference conditions for Southeast eco-region lakes were given as follows: TP 0.020-0.025 mg/L, TN 0.55-0.65 mg/L, Chl-a 1.6-2.50 mg/m 3 , SD 2.00-2.50 m.…”

The state of global scientific literature on chlorophyll-A

“…The Chl-a pigment captures photons (pigment-antenna), and is present in all living things that perform oxygenic photosynthesis (BJORN et al, 2009). Quantification of Chl-a has been used as a tool in various fields of knowledge, including bioenergy (SKJANES et al, 2007), biotechnology (KOZIOL et al, 2007), botany (THOMAS et al, 2001), ecotoxicology (PEREZ et al, 2008;SUBASHCHANDRABOSE et al, 2011;RIANO et al, 2012), marine ecology (HAWES et al, 2012;THOMAS et al, 2001), limnology (WETZEL, 2001;HUO et al, 2012), remote sensing (NOVOA et al, 2011;GURLIN et al, 2011) and agriculture (KRAUSE et al, 2010;ZHANG et al, 2010;FERNANDEZ-JARAMILLO et al, 2012).…”