DOI: 10.5061/dryad.pzgmsbcqn
title: Data from: Aquatic ecosystem responds differently to press and pulse nutrient disturbances as revealed by a microcosm experiment

description: Due to climate change and increasing anthropogenic activities, lakes are
 disturbed frequently, usually by press (e.g., diffused pollution, rising
 temperatures) or pulse (e.g., storms, rainfall, pollution events)
 disturbances. Both press and pulse disturbances can affect abiotic and
 biotic environments, changing the structure of ecosystems and affecting
 ecosystem services. To confront with the effects of climate change and
 increasing anthropogenic activities, understanding the different effects
 of press and pulse disturbances on lake ecosystems is essential. This
 study assessed the effect of press and pulse disturbances of phosphorus on
 a microcosmic aquatic ecosystem by measuring the total phosphorus (TP),
 algae density, and physiological indicators of submerged macrophytes. We
 found that the microcosmic aquatic ecosystem responded differently to
 press and pulse disturbances. Our results suggested that it had a lower
 resistance to pulse phosphorus disturbances than to press phosphorus
 disturbances. There were significantly higher nutrient concentrations and
 algal densities in the pulse treatment than in the press treatment.
 Positive feedback was found between the biomass of submerged macrophytes
 and the water quality. There was a higher submerged macrophytes biomass at
 low TP concentration and algal density. In the context of climate change,
 press and pulse disturbances could have severe impacts on lake ecosystems.
 Our findings will provide some insight for further research and lake
 management.
description: Water samples 20 cm
 below the water surface were collected once a day in all treatments. TP
 concentrations in the water column were measured using combined persulfate
 digestion. The optical density 680 (OD680) value, which represents the
 algal density, was measured at a wavelength of 680 nm using an
 ultraviolet–visible spectrophotometer. After 30 days, intact plants were collected and washed for laboratory determination of indicators. Each individual plant was carefully collected, and the epiphyton was separated from the macrophyte using a small brush in the laboratory. Filamentous algae were collected with a scraper from the walls of the aquariums and dried naturally on foil. Weight and root/shoot were expressed in fresh weight. Peroxidase (POD), catalase (CAT), and superoxide dismutase (SOD) were extracted from fresh <em>V. natans</em> tissues. The enzymatic content of <em>M. spicatum</em> was not analyzed, due to insufficient fresh weight for grinding. POD activity was determined by an increase in absorbance at a wavelength of 470 nm due to guaiacol oxidation. The unit of CAT activity was defined as the amount of enzyme that decomposed 1 μmol H<sub>2</sub>O<sub>2</sub> per minute . SOD activity was measured using the method described by Ewing and Janero.   We obtained 3 mL water samples (20 cm below the water surface) from the experimental aquariums each day. The samples were dark-acclimated for 15 minutes. The minimum fluorescence (<em>F</em><sub>0</sub>) value and the maximum fluorescence (<em>F</em><sub>m</sub>) value were measured by a Phyto-PAM (Walz, Germany). The difference between the <em>F</em><sub>m</sub> and <em>F</em><sub>0</sub> values is the variable fluorescence (<em>F</em><sub>v</sub>). Then the maximum photochemical efficiency of photosystem II (<em>F</em><sub>v</sub>/<em>F</em><sub>m</sub>) was measured.