基于营养盐限制调控的藻华控制及生态修复技术

Nutrient Limitation-Based Techniques for Algal Bloom Control and Ecological Restoration

摘要

人为氮和磷营养盐的输入导致很多大型湖库发生不同程度的富营养化，严重威胁了饮用水安全和水生态系统的可持续性。判定浮游藻类生长繁殖的限制性营养盐并对其进行调控，能够有效地控制藻华暴发，从而恢复健康的生态系统。2021年10月，本研究在太湖梅梁湾实验塘实施了改性当地土壤（Modified Local Soil，MLS）生态修复技术，通过4组不同季节的营养盐原位添加实验结合长期监测，考察MLS技术实施后浮游植物生长营养盐限制的变化和生态系统恢复情况。与3#对照塘相比，4#处理塘因MLS技术的实施，总氮（TN）、总磷（TP）、溶解性无机氮（DIN）和溶解态活性磷（SRP）等营养盐被去除，至使浮游植物生长由不受氮和磷限制转变为磷限制，且磷限制阈值为0.2mg·L^-1；6个月后（2022年3月），4#处理塘依然保持磷限制，由于春季SRP浓度有所提升，磷限制阈值降为0.1mg·L^-1，虽然3#对照塘也表现为磷限制，但在相同磷（0.1mg·L^-1）供应下所达到的最大Chl-a浓度为处理塘的1.8倍；进入夏季后（2022年6月），4#处理塘和3#对照塘均由磷限制转变为氮限制，磷为第二限制性营养盐，由于4#处理塘浮游植物种类增加，喜高氮和磷的绿藻和硅藻占比达44%，因此，4#处理塘氮限制阈值（1.0mg·L^-1）高于以蓝藻为主的3#对照塘（0.5mg·L^-1）；冬季期间，尽管两塘均展现出氮和磷共同限制，但4#处理塘内依然保持绿藻、硅藻和隐藻等多种藻类并存状态，单一藻类暴发的可能性不大，而3#对照塘内以微囊藻为主的蓝藻大量存在，增加了春季蓝藻暴发风险。本研究表明，MLS技术可在短期内快速去除水体中的藻华，降低氮、磷营养盐浓度，将浮游植物生长由不受氮和磷限制转变为单一磷限制。从长期效应来看，由于MLS处理后的水体中沉水植物大量恢复，其与藻类生长竞争吸收营养盐，还能通过化感作用抑制藻类生长，使水体中的浮游植物由蓝藻为优势种群转变为多种浮游植物共存的状态；同时，营养盐浓度降低和浮游植物群落结构改变，使得氮和磷均成为限制性营养盐，进而抑制了蓝藻水华暴发；最终，以藻类为优势地位的藻华水体逆转为以沉水植被为主的健康水体，提升了氮磷营养盐的环境容量。本研究为藻华快速去除、生态系统恢复以及营养盐管理策略制定，提供了有效的技术手段，同时也为突发性外源氮、磷营养盐输入引发的藻华暴发等水生态系统环境损害，提供了快速可行的判定技术方法。

Abstract

Excessive anthropogenic inputs of nitrogen (N) and phosphorus (P) led to varying degrees of eutrophication in many large lakes and reservoirs, seriously threatening drinking water safety and the sustainability of aquatic ecosystems. Identification and regulation of limiting nutrients for phytoplankton growth were considered effective strategies to control algal blooms and restore ecosystem health. In October 2021, Modified local soil (MLS) technique was implemented in experimental ponds in Meiliang Bay, Lake Taihu. Four sets of seasonal in situ nutrient addition experiments combined with long-term monitoring were conducted to evaluate changes in phytoplankton nutrient limitation and ecosystem recovery after MLS application. Compared with the control (No.3), after MLS treatment, the removal of nutrients including total nitrogen (TN), total phosphorus (TP), dissolved inorganic nitrogen (DIN), and soluble reactive phosphorus (SRP) caused the growth of phytoplankton to shift from being non-limited by N and P to being P-limited, with a P limitation threshold of 0.2 mg·L^-1. After six months (spring, Mar. 2022), the treated pond (No.4) still exhibited P limitation, but the threshold declined to 0.1 mg·L^-1 because of elevated SRP. Although the control pond (No.4) also showed P limitation, its maximum Chl-a concentration under the same P supply (0.1 mg·L^-1) was 1.8 times higher than that in the treated pond. In summer (Jun. 2022), both ponds shifted from P limitation to N limitation, with P acting as a secondary limiting nutrient. In the treatment pond (No.4), phytoplankton diversity increased, and green algae and diatoms (44% of the community) replaced cyanobacteria dominance, leading to a higher N limitation threshold (1.0 mg·L^-1) compared with the control pond (0.5 mg·L^-1). In winter, although both ponds exhibited N and P co-limitation, the treatment pond (No. 4) maintained a mixed community of green algae, diatoms, and cryptophytes, reducing the likelihood of single-species blooms. By contrast, the control pond remained dominated by Microcystis, creating a higher risk of cyanobacterial blooms in the following spring. Overall, MLS rapidly removed algal blooms and reduced N and P concentrations in the short term, shifting phytoplankton growth from non-limitation to P limitation. In the long term, submerged macrophytes restored substantially in the treatment pond, competing with algae for nutrients and suppressing algal growth through allelopathy. Consequently, the auqatic ecosystem shifted from cyanobacteria dominance to coexistence of diverse phytoplankton, nutrient concentrations declined, and both N and P became limiting nutrients. This transition suppressed cyanobacterial blooms and transformed an algal-dominated system into a macrophyte-dominated healthy ecosystem, thereby enhancing the environmental carrying capacity for N and P. This study provided an effective approach for rapid algal bloom removal, ecosystem restoration, and the development of nutrient management strategies. In addition, a rapid and feasible method was provided for assessing potential algal bloom outbreaks and associated environmental damage to aquatic ecosystems resulting from sudden external inputs of nitrogen and phosphorus.

关键词

改性当地土壤 / 营养盐限制 / 浮游植物 / 沉水植被 / 太湖

Key words

modified local soil / nutrient limitation / phytoplankton community structure / submerged macrophytes / Lake Taihu

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