Data from: Effects of macrophytes on lake‐water quality across latitudes: a meta‐analysis

Macrophytes are widely recognized for improving water quality and
stabilizing the desirable clear‐water state in lakes. The positive effects
of macrophytes on water quality have been noted to be weaker in the
(sub)tropics compared to those of temperate regions. We conducted a global
meta‐analysis using 47 studies that met our set criteria to assess the
overall effects of macrophytes on water quality (measured by phytoplankton
chlorophyll a concentration, total nitrogen concentration, total
phosphorus concentration, Secchi depth, and the trophic state index) and
to investigate how these effects correlate with latitude using
meta‐regressions. We also examined if the effects of macrophytes on
lake‐water quality differ with growth form in (sub)tropical and temperate
areas by grouping the data and then comparing the effect sizes. We found
that macrophytes significantly reduced phytoplankton chlorophyll a
concentration, total nitrogen concentration, total phosphorus
concentration, as well as the trophic state index, but they did not have a
significant overall effect on Secchi depth. The effects of macrophytes on
reducing phytoplankton chlorophyll a concentration, total nitrogen
concentration, and the trophic state index did not differ with latitude.
However, the reduction of total phosphorus concentration was greater at
lower latitudes. We showed that at lower latitudes, the positive effects
of macrophytes on water quality are similar to or greater than those at
higher latitudes, thus challenging the prevailing paradigm of macrophytes
being less effective at enhancing lake‐water quality in the (sub)tropics.
Furthermore, our data showed that the macrophyte effects vary by growth
forms, and the growth forms that positively affect water quality differ
between the (sub)tropical and temperate areas. We showed a lack of
significant macrophyte effects in surveys within and outside macrophyte
stands, suggesting difference in the sensitivities of study designs or
possibly weaker effects of macrophytes in lakes compared to experimental
settings.