Reference and current Trophic Level Index of New Zealand lakes: benchmarks to inform lake management and assessment

Abstract

Benchmarks to inform lake management and assessment Knowledge of trophic status is fundamental to understanding the condition and function of lake ecosystems. We developed regression models to predict chlorophyll a concentrations (chl a) in New Zealand lakes for reference and current states, based on an existing dataset of total nitrogen (TN) and total phosphorus (TP) concentrations for 1,031 lakes. Models were then developed to predict Secchi depth based on chl a and a sediment resuspension term applicable to shallow lakes. Estimates of all four Trophic Level Index (TLI) variables (chl a, TN, TP and Secchi depth) were analysed to estimate reference and current state TLI for the nationally representative sample of 1,031 lakes. There was a trend of eutrophication between reference and current states, with systematic differences among lake geomorphic types. Mean chl a increased 3.5-fold (2.42 mg m-3 vs. 8.32 mg m-3) and mean Secchi depth decreased (indicating lower clarity) by approximately one-third (9.62 m vs. 6.48 m) between reference and current states. On average, TLI increased by 0.67, with the TLI increase >1 in approximately one-third (31%) of lakes. This study informs the status of lake ecosystems in NZ and provides benchmarks to guide management and assessment.

Using palaeolimnology to guide rehabilitation of a culturally significant lake in New Zealand

“…(willow), were introduced. These changes in land cover, together with changing agricultural practices and urbanization, have resulted in the widespread degradation of many freshwater ecosystems across New Zealand (Abell et al, 2020).…”

Spatio-temporal evolution of eutrophication and water quality in the Turawa dam reservoir, Poland

“… Reference@Trophic status Vollenweider (1965) Sakamoto (1966) EPA survey (1974) Carlson and Simpson (1996) Oligotrophic < 10 < 20 < 10 < 6 Oligo-mesotrophic 10–20 – – 6–12 Mesotrophic 20–50 20–50 10–20 12–24 Mesoeutrophic 50–100 – – 24–48 Eutrophic > 100 > 50 > 20 48–96 Hipereutrophic – – – > 96 where DL P is dangerous load of phosphorus [g/m 2 year]; AL P is actual phosphorus load [g/m 2 year] (AL P = ; where Q mean is average annual flow [l/year], and A is reservoir area [m 2 ]); DL N is dangerous load of nitrogen [g/m 2 year] (the value of 2.0 was assumed, according to the Kajak method (2001)); and AL N is actual nitrogen load [g/m 2 year] (AL N = ; where C N is average annual nitrogen concentration [g/l]). Trophic Level Index (TLI) 65 – 67 is calculated using formulas ( 7 – 11 ) that use the average results for the following parameters: total nitrogen (TN) (TL N index), total phosphorus (TP) (TL P index), water transparency measured with a Secchi disc (TS) (TL S index), and chlorophyll a (TC) (TL C index). The overall score is expressed on a scale of 0 to 9 and is assessed based on the scale shown in Table 4 : …”

“… Trophic Level Index (TLI) 65 – 67 is calculated using formulas ( 7 – 11 ) that use the average results for the following parameters: total nitrogen (TN) (TL N index), total phosphorus (TP) (TL P index), water transparency measured with a Secchi disc (TS) (TL S index), and chlorophyll a (TC) (TL C index). The overall score is expressed on a scale of 0 to 9 and is assessed based on the scale shown in Table 4 : …”

Environmental Characterization of Two Ecologically Distinct Gangetic Oxbow Lakes using Zooplankton Taxonomic Indices Through Comparative Approach for Wetland Monitoring

“…Various environmental factors are applied to measure the trophic status of a lake. One of the most widely used trophic status indices for classifying lakes based on total phosphorus (TP), Sechhi depth (SD) and concentration of Chl a is Carlson trophic status index (Carlson and Havens, 2005;Abell et al, 2020). Chlorophyll a concentration proxies the phytoplankton biomass which directly involves in signifying the production functions of aquatic ecosystem .…”