Numeric Nutrient Criteria (NNC) - Stream Nutrient Regions

As part of the analyses conducted to derive nutrient standards for streams, the Department evaluated the available nutrient data for regional differences and ultimately developed a regionalization criteria for the stream nutrient standards. Nutrient Watershed Regions are drainage areas over which the stream nutrient thresholds in paragraph 62-302.531(2)(c), F.A.C., apply. For purposes of interpreting the numeric nutrient criteria (NNC) in paragraph 62-302.530(47)(b), F.A.C., under paragraph 62-302.531(2)(c), F.A.C., a “stream” is defined as a predominantly fresh surface waterbody with perennial flow in a defined channel with banks during typical climatic and hydrologic conditions for its region within the state. During periods of drought, portions of a stream channel may exhibit a dry bed, but wetted pools are typically still present during these conditions. Streams do not include: (a) non-perennial water segments where fluctuating hydrologic conditions, including periods of desiccation, typically result in the dominance of wetland and/or terrestrial taxa (and corresponding reduction in obligate fluvial or lotic taxa), wetlands, or portions of streams that exhibit lake characteristics (e.g., long water residence time, increased width, or predominance of biological taxa typically found in non-flowing conditions), or tidally influenced segments that fluctuate between predominantly marine and predominantly fresh waters during typical climatic and hydrologic conditions; or (b) ditches, canals and other conveyances, or segments of conveyances, that are man-made, or predominantly channelized or predominantly physically altered; and 1) are primarily used for water management purposes, such as flood protection, stormwater management, irrigation, or water supply; and 2) have marginal or poor stream habitat or habitat components, such as a lack of habitat or substrate that is biologically limited, because the conveyance has cross sections that are predominantly trapezoidal, has armored banks, or is maintained primarily for water conveyance. The NNC Implementation Document (http://www.flrules.org/Gateway/reference.asp?No=Ref-02905) provides additional information describing the information and data needed to determine the applicable freshwater criteria (i.e., stream, springs, lakes, or narrative).为制定溪流营养物标准开展相关分析工作期间，相关部门对现有营养物数据的区域差异开展了评估，并最终制定了溪流营养物标准的区域划分准则。营养物流域区（Nutrient Watershed Regions）是指适用《佛罗里达行政规章》（F.A.C.）第62-302.531(2)(c)款溪流营养物阈值的汇水区域。为便于依据《佛罗里达行政规章》（F.A.C.）第62-302.531(2)(c)款解读《佛罗里达行政规章》（F.A.C.）第62-302.530(47)(b)款规定的数值型营养物标准（numeric nutrient criteria, NNC），本次分析将"溪流"定义为：该州对应区域内，在典型气候与水文条件下，于具有固定岸堤的河道中常年流动的以淡水为主的地表水体。干旱时期，部分河道床面可能裸露干涸，但此时通常仍存在浸润水塘。以下情形不属于溪流范畴：(a) 因水文条件波动（包括长时间干涸），通常以湿地和/或陆生生物类群为主（相应地，专性河流或流水生物类群占比降低）的非常年性水体区段、湿地，或呈现湖泊特征的溪流区段（例如水力停留时间长、河道宽度增加，或以静水环境典型生物类群为主），以及在典型气候与水文条件下，在以海水为主和以淡水为主之间往复变化的受潮汐影响河段；或(b) 人工修建的沟渠、运河及其他输水设施，或经主要渠化或物理改造的输水区段，且同时满足以下两项条件：1) 主要用于水资源管理用途，如防洪、雨水管理、灌溉或供水；2) 溪流生境或生境组成较差，例如缺乏具备生物适宜性的栖息地或底质，原因在于该输水设施的断面多为梯形、岸坡经加固处理，或其维护目的仅为输水。《数值型营养物标准实施文件》（NNC Implementation Document，http://www.flrules.org/Gateway/reference.asp?No=Ref-02905）提供了更多信息，详述了确定适用淡水标准（即溪流、泉水、湖泊或叙述型标准）所需的信息与数据。