Macrophyte depth limits in North Island (New Zealand) lakes of differing clarity

Abstract

The seasonal variation in water clarity, as indicated by the attenuation coefficient for photosynthetically active radiation, Kd (m-1), was determined by monthly measurements for a year in 9 North Island, New Zealand lakes. Kd varied by a factor of 2 to 3 in 8 of the lakes, and a factor of 5 in one. Annual mean Kd (symbol% MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaam4saaaa!36BD!\[K\] d) varied by a factor of approximately 15 between lakes. The maximum depth of water colonized by macrophytes (zc)was also determined. Values of zc were in the range 1.5–12.5 m. The relationship zc=4.34/% MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaam4saaaa!36BD!\[K\]d accounted for most (93 percent) of the variability in zc, indicating that average annual clarity was probably a useful predictor of zc in lakes in this region. The values of zc in these North Island lakes were generally greater than values calculated using previously published empirical relationships derived for northern hemisphere groups of lakes. The extent to which these relationships underestimated zc in the North Island lakes was broadly related to latitude. Estimated average irradiance at zc in each lake was similar to compensation point irradiances reported previously for freshwater macrophytes.