water Article Decline of the Maurepas Swamp, Pontchartrain Basin, Louisiana, and Approaches to Restoration Gary P. Shaffer 1,2,3,*, John W. Day 2,4, Demetra Kandalepas 1,3, William B. Wood 1, Rachael G. Hunter 2, Robert R. Lane 2,4 and Eva R. Hillmann 1 1 Department of Biological Sciences, Southeastern Louisiana University, Hammond, LA 70402, USA; [email protected] (D.K.); [email protected] (W.B.W.); [email protected] (E.R.H.) 2 Comite Resources, Inc. 11643 Port Hudson Pride Rd., Zachary, LA 70791, USA; [email protected] (J.W.D.); [email protected] (R.G.H.); [email protected] (R.R.L.) 3 Wetland Resources, LLC, 17459 Riverside Lane, Tickfaw, LA 70466, USA 4 Department of Oceanography and Coastal Sciences, Louisiana State University, Baton Rouge, LA 70803, USA * Corresponding: [email protected]; Tel.: +1-985-549-2865; Fax: +1-985-549-3851 Academic Editor: Luc Lambs Received: 14 November 2015; Accepted: 24 February 2016; Published: 15 March 2016 Abstract: The Maurepas swamp is the second largest contiguous coastal forest in Louisiana but it is highly degraded due to subsidence, near permanent flooding, nutrient starvation, nutria herbivory, and saltwater intrusion. Observed tree mortality rates at study sites in the Maurepas swamp are very high (up to 100% tree mortality in 11 years) and basal area decreased with average salinities of <1 ppt. Habitat classification, vegetation productivity and mortality, and surface elevation changes show a clear trajectory from stagnant, nearly permanently flooded forests with broken canopy to degraded forests with sparse baldcypress and dominated by herbaceous species and open water to open water habitat for most of the Maurepas swamp without introduction of fresh water to combat saltwater intrusion and stimulate productivity and accretion. Healthy forests in the Maurepas are receiving fresh water containing nutrients and sediments from urban areas, high quality river water, or secondarily treated municipal effluent. Currently, two proposed diversions into the swamp are via Hope Canal (57 m3¨ s´1) and Blind River (142 m3¨ s´1). These diversions would greatly benefit their immediate area but they are too small to influence the entire Maurepas sub-basin, especially in terms of accretion. A large diversion (>1422 m3¨ s´1) is needed to deliver the adequate sediments to achieve high accretion rates and stimulate organic soil formation. Keywords: Taxodium distichum—Nyssa aquatica swamp; coastal forested wetlands; hydrologic alteration; saltwater intrusion; Mississippi River diversion 1. Introduction The lower Mississippi Delta, defined herein as the area south of the confluence of the Atchafalaya and Mississippi Rivers, is one of the most important coastal ecosystems, both ecologically and economically, in North America. However, it is severely degraded and is threatened with collapse unless wide-scale restoration efforts are undertaken [1]. During the 20th century, about 25% of the coastal wetlands in the Delta, approximately 4800 km2, were lost through conversion to open water [2–5]. A variety of factors led to this wetland loss including pervasive hydrological alteration, enhanced subsidence due to petroleum extraction, saltwater intrusion, and barrier island deterioration, but perhaps the most important was the almost complete elimination of riverine input to the deltaic plain due to flood control levee construction and closure of distributaries that connected the Mississippi River to the surrounding Delta prior to the 19th century [1,6,7]. The State of Louisiana has embarked on an ambitious $50 billion, 50-year restoration master plan of the Delta that focuses primarily on restoration of marshes and barrier islands [8]. There are, Water 2016, 8, 101; doi:10.3390/w8030101 www.mdpi.com/journal/water Water 2016, 8, 101 2 of 28 however, about 324,000 hectares of freshwater forested wetlands in the coastal zone. Despite the fact thatWater almost 2016, 8, all101 of these forested wetlands are degraded and non-regenerative [9–212 of], 28 little of the Master Plan addresses forested wetlands. Freshwater forests are an important component of the MississippiThe Delta. State Dominated of Louisiana by has baldcypress-water embarked on an ambitious tupelo (Taxodium $50 billion, distichum 50-year -restorationNyssa aquatica master) swamps plan of the Delta that focuses primarily on restoration of marshes and barrier islands [8]. There are, and bottomland hardwood wetlands, these forests reduce nutrients and sediments in surface water however, about 324,000 hectares of freshwater forested wetlands in the coastal zone. Despite the fact that ultimatelythat almost flows all of into these the forested Gulf, providewetlands wildlifeare degraded habitat, and protectnon-regenerative coastal urban[9–12], little areas of from the storm damageMaster by reducing Plan addresses storm surgeforested and wetlands. eliminating Freshwat waveser forests atop are the an surge, important retain component stormwater, of the recharge groundwater,Mississippi support Delta. timber, Dominated fish, by fur, baldcypress-water and alligator harvests, tupelo ( offerTaxodium opportunities distichum-Nyssa for recreation,aquatica) and sequesterswamps carbon and [9 –bottomland11,13,14]. Costanzahardwoodet wetlands, al. [15] estimated these forests the reduce value ofnutrients ecosystem and servicessediments worldwide in and determinedsurface water that that swamps ultimately and flows floodplains into the hadGulf the, provide second wildlife highest habitat, economic protect value coastal ($7927 urban per acre areas from storm damage by reducing storm surge and eliminating waves atop the surge, retain per year),stormwater, second only recharge to coastal groundwater, estuaries support ($9248 timber, per fish, acre fur, per and year). alligator Batker harvests,et al. offer[14 ]opportunities estimated that the value offor ecosystem recreation, servicesand sequester of coastal carbon forested[9–11,13,14]. wetlands Costanza in et the al. [15] Mississippi estimated Deltathe value was ofbetween ecosystem $3.3 and $13.3 billionservices per worldwide year. and determined that swamps and floodplains had the second highest economic Thevalue Maurepas ($7927 per swamp acre per is year), the second only largest to coastal contiguous estuaries ($9248 coastal pe forestr acre per in year). Louisiana, Batker et containing al. 776 km[14]2 of estimated freshwater that forested the value wetlands,of ecosystem and services about of 52coastal km2 forestedof fresh wetlands and oligohaline in the Mississippi marshes [16]. Delta was between $3.3 and $13.3 billion per year. This swamp is highly degraded due to subsidence, permanent flooding, lack of mineral sediment The Maurepas swamp is the second largest contiguous coastal forest in Louisiana, containing and nutrient776 km input,2 of freshwater nutriaherbivory, forested wetlands, and saltwater and about intrusion 52 km2 of from fresh Lakeand oligohaline Pontchartrain marshes during [16]. severe storms andThis drought.swamp is Observedhighly degraded tree mortalitydue to subsidence, rates at studypermanent sites flooding, in the Maurepas lack of mineral swamp sediment are very high (up to 100%and nutrient tree mortality input, nutria in 11 herbivory, years for and some saltwater plots), intrusionand at from these Lake rates Pontchartrain the trees willduring be severe largely gone by midstorms century and [10 drought.]. Observed tree mortality rates at study sites in the Maurepas swamp are very Thehigh Maurepas (up to 100% swamp tree mortality is located in in11 theyears Pontchartrain for some plots), Basin, and at a these 12,000-km rates the2 watershedtrees will be encompassinglargely gone by mid century [10]. 16 Louisiana parishes that is the most densely populated region in Louisiana and includes both metro The Maurepas swamp is located in the Pontchartrain Basin, a 12,000-km2 watershed New Orleansencompassing and Baton16 Louisiana Rouge parishes (Figure that1). is About the most 2.1 densely million populated people region live in in theLouisiana Basin and or over a third ofincludes the total both Louisiana metro New population Orleans and [Baton17]. Historically,Rouge (Figure 1). the About upper 2.1 Pontchartrainmillion people live Basin in the was 90% baldcypress-waterBasin or over tupeloa third (ofTaxodium the total distichum-NyssaLouisiana population aquatica [17]. )Historically, swamp [18 the], butupper within Pontchartrain the last several decadesBasin there was has 90% been baldcypress-water a significant transitiontupelo (Taxodium from distichum-Nyssa forested to emergent aquatica) swamp wetlands [18], duebut within to increased the last several decades there has been a significant transition from forested to emergent wetlands salinities and saltwater intrusion events associated with leveeing of the Mississippi River and cessation due to increased salinities and saltwater intrusion events associated with leveeing of the Mississippi of riverineRiver inputs and cessation of fresh of water riverine [6 inputs,7,11,12 of ].fresh water [6,7,11,12]. Figure 1. General location of the Maurepas swamp (yellow circle) within the Pontchartrain Basin, southeastern Louisiana. Figure modified from Lake Pontchartrain Basin Foundation 2015 Water Quality Brief. Water 2016, 8, 101 3 of 28 Construction of deep navigation and access canals, such as the Mississippi River Gulf Outlet (MRGO) [11], combined with sea level rise, has exacerbated the frequency and intensity of saltwater intrusion events. Periodic droughts can