Restoration of the turning basin and tidal wetlands at Saugus Iron Works National Historic Site: Summary data report for 2004 to 2014 monitoring

James, Mary-Jane

In 2007, the National Park Service initiated a restoration program at Saugus Iron Works National Historic Site (SAIR) to restore the historic turning basin and wetland area adjacent to the Saugus River. To fulfill regulatory requirements and enhance understanding of tidal freshwater wetland restoration practices, an intensive pre- and post-restoration monitoring program was implemented. This report summarizes monitoring data collected prior to the restoration (2004) and the six years (2008 to 2014) following the restoration, and includes summaries for vegetation, nekton, and wildlife observations. The purpose of this report is to present the data with only limited data analyses and interpretation provided. Several sections of this report were retained from the 2008-2012 Final Report (James-Pirri 2013) that provided statistical analyses of some monitoring variables from 2004 to 2012 (e.g., vegetation and nekton) and also incorporated findings from CH2MHill surveys (e.g., water quality, benthic invertebrates). Note that this is only an INTERIM report and results and interpretation may change pending the collection of future monitoring data. The Final Report, scheduled for submission in the fall of 2017, will provide extensive statistical analyses, interpretation, and syntheses for all monitoring years (2004 to 2016). Information contained herein are to inform stakeholders of the progress of the restoration monitoring, summarize monitoring data, document pertinent findings, and to assist with any adaptive management plans or actions associated with the restoration. The restoration of the historic turning basin and wetlands succeeded in removing invasive vegetation and establishing a tidal mud flat/low marsh along the Saugus River. After restoration (2009-2012), the dominant plant on the restored marsh was dwarf spike rush (Eleocharis parvula) a native plant tolerant of fresh to brackish water conditions; however, in recent years (2013-2014) the abundance of this plant has decreased and bare ground/algal mat has increased. The upland edge of the restored marsh had a diverse assemblage of wetland plants. The dominant aquatic plant in the river was horned pondweed (Zannichella palustris) which has gradually increased in cover since the restoration. This aquatic plant is also commonly found in the turning basin, along with other submerged aquatic species. Some invasive plants have been observed in the restoration area since 2008, with the most notable being purple loosestrife (Lythrum salicaria). Since the restoration, the nekton community in the Saugus River has transitioned from a mostly freshwater community to a brackish-estuarine community. Common nekton include four-spine stickleback (Apeltus quadracus), white sucker (Catostomus commersoni), and mummichog (Fundulus heteroclitus). In the turning basin, young-of-the-year American eel (Anguilla rostrata) were common in all years. The mummichog (Fundulus heteroclitus) has become increasingly abundant in recent years. A few individuals of freshwater species were still sampled each year (e.g., largemouth bass [Micropterus salmoides], redfin pickerel [Esox americanus americanus]). Upstream movement of tidal estuarine water has occurred since the restoration, especially during high tides and periods of low river flow. The intrusion of saline water to the upper reach of the Saugus River at SAIR is likely a primary factor responsible for the change from a primarily freshwater nekton community (before the restoration) to a brackish/estuarine community in the years following the restoration.

Restoration of the turning basin and tidal wetlands at Saugus Iron Works National Historic Site: Summary data report for 2004 to 2014 monitoring

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