Response of chlorophyll a to total nitrogen and total phosphorus concentrations in lotic ecosystems: a systematic review

Abstract Background Eutrophication of freshwater ecosystems resulting from nitrogen and phosphorus pollution is a major environmental stressor across the globe. In this systematic review, we compiled synthesized literature on sestonic benthic chlorophyll (chl-a) responses to total (TN) (TP) concentrations in water column streams rivers provide state-of-the-science summary nutrient impacts these endpoints. This review was motivated by need for comprehensive information stressor-response relationships most common biotic response measures used state-level managers United States assess eutrophication lotic support decision making. Methods Searches peer-reviewed non-peer-reviewed articles were conducted using bibliographic databases, specialist websites, search engines. These returns supplemented with citation mapping requests material experts. Articles screened relevance pre-determined eligibility criteria, risk bias evaluated each included article based study type-specific criteria. Narrative summaries meta-analysis evaluate four primary relationships: TN-benthic chl-a, TP-benthic TN-sestonic TP-sestonic chl-a. Potential effects modifying factors validity conclusions assessed via sensitivity sub-group analysis meta-regression. Results Meta-analysis 105 articles, representing 439 cause-effect pairs, showed that mean effect sizes both chl-a TN TP positive. Of examined, had positive relationship, followed For individual U.S. states, mostly positive, few exceptions. Chlorophyll measurement method moderately significant influence size responding more strongly if fluorometry versus spectrophotometry used. Year publication negative size, as did concentration relationships. When same measured TP, tended respond similarly nutrients. Sensitivity indicated are robust studies high bias. Conclusions confirms nutrients consistently impact producer biomass worldwide. It builds previous syntheses evaluating positively range stream river conditions, but also points limits (e.g., potential saturation at concentrations). Lack consistent reporting contextual data limited our ability examine how moderating influenced Overall, responsible protecting quality evidence base column.