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Four decades of diluting phosphorus to maintain lake quality
Author(s) -
Welch Eugene B.,
Brattebo Shan K.,
Overland Christopher
Publication year - 2020
Publication title -
water environment research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.356
H-Index - 73
eISSN - 1554-7531
pISSN - 1061-4303
DOI - 10.1002/wer.1207
Subject(s) - cyanobacteria , phosphorus , nutrient , environmental science , zoology , dilution , chlorophyll a , water quality , phytoplankton , eutrophication , microcystis , spring (device) , volume (thermodynamics) , hydrology (agriculture) , chemistry , biology , ecology , botany , geology , physics , genetics , geotechnical engineering , organic chemistry , bacteria , thermodynamics , quantum mechanics
Dilution with low‐nutrient Columbia River Water (CRW) has markedly improved Moses Lake quality for 42 years. There were two phases of CRW volume input, which proportionately lowered total phosphorus (TP). Initially, spring–summer inputs averaged 130 × 106 m 3 during 1977–1988 reducing average TP from 152 to 65 µg/L in half the lake proximal to the inputs. That input represented 1.5 volumes of that half‐lake volume. Inputs doubled through the mid‐1990s, and nearly 2.5 times since 2000, decreasing TP to a 18‐year average of 24 µg/L. Chlorophyll a (chl) decreased further from 18 µg/L during the early dilution years to about 6 µg/L as TP declined. Cyanobacteria biovolume declined to 57% of total biovolume during 1977–1988 from 98% before dilution. Less (65%) CRW water since 2016 led to higher TP (41 µg/L) and chl (18 µg/L) in 2018, while cyanobacteria averaged 87% of total biovolume. More TP and cyanobacteria in 2018 are attributed to more internal TP loading. Increased N:P ratios have possibly given more advantage to the non‐N‐fixing cyanobacteria Microcystis , which comprised 82% and 74% of maximum cyanobacteria biovolume in 2017 and 2018. Practitioner points Lake total phosphorus (TP) was reduced 57% in the 1970s–1980s by adding large volumes of low‐nutrient Columbia River water (CRW). Total P was further reduced by 65% since 2000 by more than doubling the earlier CRW input to an average spring–summer concentration of 24 μg/L. Less (65%) CRW during 2017–2018 led to higher lake TP (41 μg/L) and a worse cyanobacteria bloom in 2018. Microcystis , an non‐nitrogen fixer, was the dominant cyanobacteria in 2017–2018 likely related to higher N:P ratios.