Saco River Research Articles

Land use and land cover mapping of the Saco River’s watershed, State of Maranhão, Brazil

Land use and land cover mapping benefits landscape understanding and its changes, especially those resulting from anthropogenic actions in the physical environment. The present study aimed at mapping land use and coverage of the Saco River’s watershed (located in Codó, state of Maranhão). The area comprises the coconut forest (named Mata dos Cocais), a region that encompasses the characteristics of different biomes on the same temporal and spatial scale. The methodology applied was based on remote sensing techniques developed in a Geographic Information System (GIS) environment, processing data from Landsat 8 and supervised classification. The results showed a predominance of dense vegetation in the basin under study, in addition to a reduced occupation by classes of urban area and water bodies. The overall accuracy was 79% and dense vegetation presented a higher user and producer accuracy than the general, with 91 and 87%, respectively. On the other hand, the highest commission and omission errors were those in urban areas and water bodies, which coincided with the lowest occupation classes in the Saco River basin. These results are pioneering for the coconut forest and provide data for strategic planning of environmental actions.

The Effect of Sediment Storage in Glaciated Catchments on Multimineral Detrital Geochronology: Deciphering Conflicting Zircon and Apatite U‐Pb Dates

AbstractDetrital geochronology and thermochronology are widely used to study erosion and the exhumation of rocks. In glaciated landscapes, these studies have shown exhumation to be highly heterogeneous; however, these studies have typically only applied apatite low‐temperature thermochronology, a mineral prone to mechanical and chemical breakdown, and a method with lower precision or data dispersion. As such, it is unclear if the detrital apatite signal represents derivation from the entire catchment. In this study, we present both zircon and apatite U‐Pb dates from a modern detrital sample of the Saco River, New Hampshire, USA. The river flows through a catchment that was highly modified during the last glacial maximum. The underlying geology is characterized by two contrasting groups from different eras; Palaeozoic metasediments and granites, and Mesozoic granitoids. Zircon U‐Pb dates are consistent with near‐uniform erosion of the catchment, encompassing both Proterozoic–Palaeozoic and Jurassic–Cretaceous grains consistent with the catchment's geology. However, detrital apatite U‐Pb dates are predominantly Palaeozoic. Detrital U‐Pb modeling shows that zircon grains are indeed derived from erosion of the entire catchment, while apatites likely originate from areas at high elevation. This stark contrast in ages likely indicates apatite's fragility. Dissolution resulting from acidic soils in the river's catchment is a likely cause, though mechanical breakdown during transport is also possible. As such, the detrital apatite signal appears to only record erosion from the modern fluvial system, while zircon represents a combination of uniform erosion during glaciation and the modern fluvial system. These findings imply the detrital apatite signal is prone to significant modification in areas of sediment storage and acidic soils with implications for sediment generation in other formerly glaciated landscapes worldwide.

A Preliminary Abundance Estimate of an Atlantic Sturgeon (Acipenser oxyrinchus oxyrinchus) Contingent Within an Open Riverine System

Abundance estimates are essential for fisheries management, but estimating the abundance of open populations with low recapture rates has historically been unreliable. However, by using mark-recapture data modulated with survivability parameters obtained from analysis of acoustic telemetry data, more accurate abundance estimates can be made for species that exhibit these characteristics. One such species is the Atlantic sturgeon, for which abundance estimates were designated a research priority following precipitous population declines throughout the 20th century. We addressed this research need in the Saco River Estuary (SRE), a system where the Atlantic sturgeon has been extensively studied using mark-recapture and acoustic telemetry methods since 2009. These data were analyzed using Bayesian analysis of a Lincoln-Peterson estimator, constrained with parameters from a Cormack-Jolly-Seber model, to provide an initial abundance estimate for the system. The resulting estimate indicated that approximately 3 299 (95% Credible Interval: 1 462–6 828) Atlantic sturgeon utilize the SRE yearly, suggesting that the SRE provides critical foraging habitat to a large contingent of the species within the Gulf of Maine. The present study demonstrated the method utilized herein was effective in generating a reasonable estimate of abundance in an open system where recapture events are rare, and therefore may provide a valuable technique for supplying initial estimates of fish abundance in additional systems that display similar characteristics.

Movements of Juvenile Winter Flounder in a Southern Maine Estuary

Overfishing and habitat loss have reduced Pseudopleuronectes americanus (Winter Flounder) populations within the Gulf of Maine (GOM), and despite strict management regulations, abundance is still low. As the GOM continues to warm, there is need to characterize Winter Flounder movements in estuaries to better understand essential habitat use. To characterize movements and habitat use of Winter Flounder, we tagged 17 juvenile flounder (115–170 mm) with acoustic transmitters (Vemco V7-2x) and monitored them using passive tracking over a 4-month period between July and November 2017 in the Saco River Estuary (SRE) in southern Maine. Movement within the SRE was highly variable, with cumulative movements of individual tracked flounder varying between 0 m (e.g., detected only at the release site) and 17,016 m. Tagged flounder were most often present in moderate (15–20 °C) temperatures and salinities (18–26 ppt), and were rarely observed in the highest temperatures (>20 °C) and salinities (>26 ppt). Movements upstream and downstream by flounder appeared to be tidally driven, with most downstream movements occurring during ebb tides and upstream movements during incoming tides. In addition, large flounder moved further away from freshwater, while small flounder either stayed within the river mouth's jetties or moved upstream. The speeds of flounder movements among receiver locations (mean = 4.49 body lengths per second, SE = 0.85) were much faster than expected for flatfish, potentially facilitated by use of tides. The GOM populations of Winter Flounder may benefit from management of juvenile habitat as environmental conditions change.

LiDAR and other evidence for the southwest continuation and Late Quaternary reactivation of the Norumbega Fault System and a cross-cutting structure near Biddeford, Maine, USA

High-resolution LiDAR (light detection and ranging) images reveal numerous NE-SW-trending geomorphic lineaments that may represent the southwest continuation of the Norumbega fault system (NFS) along a broad, 30- to 50-km-wide zone of brittle faults that continues at least 100 km across southern Maine and southeastern New Hampshire. These lineaments are characterized by linear depressions and valleys, linear drainage patterns, abrupt bends in rivers, and linear scarps. The Nonesuch River, South Portland, and Mackworth faults of the NFS appear to continue up to 100 km southwest of the Saco River along prominent but discontinuous LiDAR lineaments. Southeast-facing scarps that cross drumlins along some of the lineaments in southern Maine suggest that late Quaternary displacements have occurred along these lineaments. Several NW-SE-trending geomorphic features and geophysical lineaments near Biddeford, Maine, may represent a 30-km-long, NW-SE-trending structure that crosses part of the NFS. Brittle NWSE-trending, pre-Triassic faults in the Kittery Formation at Biddeford Pool, Maine, support this hypothesis.

Shortnose sturgeon (Acipenser brevirostrum) of the Saco River Estuary: Assessment of a unique habitat

The shortnose sturgeon (Acipenser brevirostrum; SNS) is an endangered fish that thrives in large river systems along the U.S. east coast. Despite the endangered status, our understanding of this species’ ecology is limited, especially regarding the importance of smaller river systems to their recovery. In 2010, the first sighting of SNS occurred in the Saco River estuary (SRE), Maine, a proportionately smaller system to other known drainages. To investigate the habitat usage of SNS within the SRE, an on-going acoustic tagging study was initiated in 2011. In 2016, the collection of SRE abiotic data was coupled with the acoustic tagging study in an effort to establish which environmental parameters were most influential to SNS habitat preferences using Poisson regression. Aggregations of SNS in the SRE were concentrated rkm 6–8 and regression analyses revealed that water temperature, conductivity, acidity, and dissolved oxygen content were influential to these aggregations. Furthermore, SNS prey appears to be present and abundant throughout the estuary, and thus we hypothesize that SNS use the SRE as a foraging ground, but aggregate upriver due to the physiologically preferable and energetically optimal abiotic conditions.

Tidal Marshes in the Saco River Estuary, Maine: A Study of Plant Diversity and Possible Effects of Shoreline Development

abstract We surveyed plant diversity in the tidal fresh, brackish and salt marshes of the 10-km long Saco River estuary in southern Maine. We also investigated possible relationships between shoreline development in the estuary, nitrogen levels in marsh sediments, and marsh plant species composition. Plant species cover was determined in 1 m2 quadrats along transects in sixteen marsh study sites, and land cover was mapped in a 100-m buffer around each site. Nitrogen content (total nitrogen, nitrate and ammonium) of marsh sediments was measured at ten sites. Marsh porewater salinities were determined to range from 0.2±0.1 to 18.6±2.9 ppt (mean±1 SE), with species diversity the greatest in marshes where salinity was less than 8 ppt. We identified 72 vascular plant species in the estuary's marshes, including ten that are listed as threatened or of special concern in the state of Maine. Ordination results showed that the extent of development along the shoreline correlated with the variation in plant species ...

Critical Foraging Habitat of Atlantic Sturgeon Based on Feeding Habits, Prey Distribution, and Movement Patterns in the Saco River Estuary, Maine

AbstractAn overall lack of information prompted the recent listing of Atlantic Sturgeon Acipenser oxyrinchus oxyrinchus under the Endangered Species Act. Key to the restoration of the species and of particular importance is the need to characterize the use of critical habitat across the region, specifically in the Gulf of Maine, where the population was listed as threatened. Much of the research to date has focused on large river systems able to support remnant spawning populations; however, the role of small coastal river systems for Atlantic Sturgeon is not well documented. Several of these systems are being reinhabited, and to facilitate new knowledge about the Gulf of Maine population, a long‐term (2009–2014) acoustic telemetry study for 51 Atlantic Sturgeon tagged in the Saco River was evaluated. Results suggested that the majority of fish were aggregating near the natural mouth of the estuary across the 6 years. Gastric lavage samples from 163 (91 juvenile and 72 adult) fish (65.0–171.5 cm fork length) during 2013 and 2014 demonstrated that American Sand Lance Ammodytes americanus was the most common prey (the index of relative importance for 2013 and 2014 was 93.5% and 85.4%, respectively), a finding unique to this river system. In addition, benthic sediment grabs, beam trawls, otter trawls, and beach seines conducted in 2013 and 2014 indicated that the distribution of American Sand Lances was comparable to the aggregation area observed for Atlantic Sturgeon. The combined results suggest that the Saco River estuary provides critical foraging habitat imperative for the future recovery of the Gulf of Maine Atlantic Sturgeon population.Received May 24, 2016; accepted November 17, 2016 Published online February 15, 2017

Environmental variables, not Allee effects, drive patch vigor in exotic Phragmites australis stands invading the Saco River Estuary, Maine, USA

We evaluated the importance of Allee effects, defined as declines in individual fitness with low population density or size, in the spread of invasive Phragmites australis occupying a small riverine system in Maine. We also investigated the potential of hydrodynamic drivers of propagule dispersal to alleviate Allee effects. We used molecular markers to assess genotypic richness and its relationship with patch vigor, modeled as patch expansion rate, stem density, and stem height. We hypothesized that an Allee effect would create a positive relationship between genotypic richness and patch vigor, which would be bolstered under specific environmental conditions, specifically shoreline development and nutrient enrichment. Contrary to predictions, genotypic richness and patch vigor were unrelated, as were genotypic richness and seed viability. Genotypic richness varied positively with increasing low-level (i.e., residential) development, but only in the presence of vacant substrate, specifically barren sand. Genotypic richness was also positively correlated with the proximity of open freshwater. Patch vigor was driven by a combination of distance to the river mouth and available ammonium in the soil. Overall, we found relatively high genotypic richness (mean=0.464), which suggests that the Phragmites invasion of the Saco River estuary may have already advanced beyond any early Allee effects, if they occurred in this riverine system.

First Observation of YOYParalichthys dentatus(Summer Flounder) in a Southern Maine Estuary

Abstract Herein we present evidence of the first observation of YOY Paralichthys dentatus (Summer Flounder) in the Saco River estuary, ME, in June of 2012. A possible explanation for the occurrence of YOY summer flounder in this region could be range expansion, which may have destructive effects on southern Maine estuary systems. As active predators, Summer Flounder have the potential to exploit locally abundant fishes, including Pseudopleuronectes americanus (Winter Flounder) and Ammodytes americanus (American Sand Lance).

Using circulating reproductive hormones for sex determination of Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus) in the Saco River estuary, Maine.

The Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus) is a long-lived, anadromous fish species ranging from Labrador, CA to Florida, USA. In the Saco River, located in the Gulf of Maine, this species was not present during a survey study ending in 1982, but was found inhabiting the estuary in 2007. Although the reason for the return of this sturgeon to this river system remains unknown, research on basic life-history information is necessary to facilitate the conservation of this federally protected species. Given the conservation status of the species, the present study used circulating sex steroid hormones to determine the sex of 288 Atlantic sturgeon captured between 2012 and 2014 in the Saco River estuary located in the Gulf of Maine. Overall, the sex was determined for 93% of Atlantic sturgeon sampled. Mean hormone values were similar to other Atlantic sturgeon reproductive studies. The findings indicate the validity of sex steroid hormones as a singular method for sex determination in wild Atlantic sturgeon. Results also indicated a likely 1:1 (male:female) sex ratio in the system, except in 2014 when a 1:3 ratio was observed. It is not believed that the Saco River estuary is used for spawning, as several impassable dams block access to spawning habitat. However, this area might provide crucial foraging for growth and development of juveniles and a habitat for adults forgoing spawning.

Modeling Predator–Prey Linkages of Diadromous Fishes in an Estuarine Food Web

AbstractHistorically, multiple species of diadromous fishes served as a coastal food source for commercially valuable nearshore predators. However, severe declines in diadromous fish populations in the nearshore Gulf of Maine (GOM) have impacted trophic dynamics and increased pressure on other estuarine-dependent forage resources. The objective of this study was to compare the trophic positions and interspecific interactions of diadromous fishes as predators and prey in relation to current GOM forage fishes. Empirical biomass data along with diet compositions and vital rates were used to construct a static model of a representative GOM coastal food web: the Saco River estuary (SRE) in Maine. A series of sensitivity analyses based on model outputs was performed to determine the trophic role of diadromous fishes in this estuarine food web. Model results suggested that juvenile marine transients played a greater role as forage species for SRE predators than did the anadromous Blueback Herring Alosa aestivali...

Shortnose Sturgeon in the Gulf of Maine: Use of Spawning Habitat in the Kennebec System and Response to Dam Removal

AbstractEvidence has become available in this century indicating that populations of the endangered Shortnose Sturgeon Acipenser brevirostrum migrate outside their natal river systems, but the full extent and functional basis of these migrations are not well understood. Between 2007 and 2013, 40 Shortnose Sturgeon captured and tagged in four Gulf of Maine river systems migrated long distances in coastal waters to reach the Kennebec System where their movements were logged by an acoustic receiver array. Twenty‐one (20%) of 104 Shortnose Sturgeon tagged in the Penobscot River, two (50%) of four tagged in the Kennebec System, one (50%) of two tagged in the Saco River, and 16 (37%) of 43 tagged in the Merrimack River moved to a previously identified spawning site or historical spawning habitat in the Kennebec System in spring. Most (65%) moved in early spring from the tagging location directly to a spawning site in the Kennebec System, whereas the rest moved primarily in the fall from the tagging location to a wintering site in that system and moved to a spawning site the following spring. Spawning was inferred from the location, behavior, and sexual status of the fish and from season, water temperature, and discharge, and was confirmed by the capture of larvae in some years. Tagged fish went to a known spawning area in the upper Kennebec Estuary (16 events) or the Androscoggin Estuary (14 events), an historical spawning habitat in the restored Kennebec River (8 events), or two spawning areas in a single year (7 events). We have provided the first evidence indicating that Shortnose Sturgeon spawn in the restored Kennebec River in an historical habitat that became accessible in 1999 when Edwards Dam was removed, 162 years after it was constructed. These results highlight the importance of the Kennebec System to Shortnose Sturgeon throughout the Gulf of Maine.

Influence of a River Plume on the Distribution of Brachyuran Crab and Mytilid Bivalve Larvae in Saco Bay, Maine

Larvae of most coastal marine invertebrates develop through a series of pelagic stages in the inner shelf regions where they are subject to strong velocity fields, including buoyancy-driven flows from river plumes. Taxon-specific larval behavior can interact with flow fields to determine dispersal trajectories. In this study, we examined the hydrodynamic features of the Saco River plume (in the southwestern Gulf of Maine) from July to August and explored how larval behavior may alter the distribution of mytilid (i.e., Mytilus and Modiolus) bivalve larvae and three genera of brachyuran (Carcinus, Hemigrapsus, and Cancer) crab larvae in and around that plume. Hydrographic surveys (via conductivity-temperature-depth casts) and larval sampling (via plankton tows) were conducted to assess temporal and spatial variation in the horizontal and vertical distribution of larvae. The horizontal extent of the Saco River plume varied little during our study and was governed by both inertial and rotational effects. Late stage mytilid larvae were relatively homogeneously distributed in and out of the plume, while the distribution of brachyuran larvae varied among different locations, species, and larval stages. We conclude that mytilid larvae entered the plume through physical entrainment and/or upward swimming processes and could tolerate salinities associated with the plume (<25). By contrast, brachyuran larvae avoided the plume via downward swimming to avoid osmotic stress, or had perished prior to sampling.

First documented occurrences of the shortnose sturgeon (Acipenser brevirostrum , Lesueur, 1818) in the Saco River, Maine, USA

During sampling efforts to study the more abundant Atlantic sturgeon, Acipenser oxyrinchus oxyrinchus, between May of 2009 and November of 2011, four shortnose sturgeon were captured in gill nets near the mouth of the Saco River, Maine. Two of these individuals were tagged with acoustic transmitters to monitor their movement within the Saco River. Additionally, six shortnose sturgeon that had been tagged with acoustic transmitters in the Merrimack River, Massachusetts were detected on the acoustic array deployed within the Saco River and its estuary over this time period. These incidences represent the first verified documentation of shortnose sturgeon within this estuary.

Characteristics of a Shallow River Plume: Observations from the Saco River Coastal Observing System

Interest in the coastal dynamics of river plumes has mainly focused on large rivers, but plumes from the more numerous smaller rivers have important local consequences and may, in aggregate, be significant contributors to coastal circulation. We studied the dynamics of the plume from the Saco River in Saco Bay, Gulf of Maine, over a 3-year period. The transport and salinity in the region are governed by river discharge, tides, winds, and interaction with the Western Maine Coastal Current. The dynamics of the flow field vary with location within the plume and discharge. The far-field dynamics of the Saco River plume are dominated by inertial processes (hence qualifying it as a small-scale river plume), during times of low discharge, with low salinity water present both up and downstream of the river mouth, but are dominated by rotational processes during times of high discharge (thus qualifying it as a large-scale river plume), with buoyant water primarily advected downshelf. Near-field dynamics are governed by weak, subcritical flow during low discharge but strongly inertial, supercritical flow during high discharge. Offshore movement of the plume is not governed by Ekman dynamics but is instead a result of discharge, wind-induced vertical mixing, and the geography of the coastline and adjacent islands.

The Fish Assemblage Structure of the Saco River Estuary

The Saco River estuary is a narrow estuary in southern Maine, for which the fauna has not been described in nearly 30 years. Beach seining, otter trawling, and beam trawling were conducted between April and October of 2007 and 2008 to assess seasonal variation in fi sh assemblage structure. Twenty-four species were observed over the two sampling seasons, and nearly all species were at lengths indicative of juvenile age. Clu- pea harengus (Atlantic Herring), Pseudopleuronectes americanus (Winter Flounder), Anguilla rostrata (American Eel), Microgadus tomcod (Atlantic Tomcod), Pomatomus saltatrix (Bluefi sh), and Osmerus mordax (Rainbow Smelt) are either commercially or recreationally valuable, while Acipenser oxyrynchus oxyrynchus (Atlantic Sturgeon), Alosa aestivalis (Blueback Herring), and Rainbow Smelt are federally listed species of concern. Substantial historical assemblage changes were observed, including both the loss of commercially important species and the addition of species of concern. Regular monitoring of estuarine habitats is necessary to identify changes in assemblages and to better understand potential drivers of ecosystem change.

Observations on the Distribution of Ichthyoplankton within the Saco River Estuary System

Determining planktonic larval species composition and abundance data can serve to elucidate local patterns of distribution, determine an area's importance as a nursery ground, and help clarify broad-scale trends of adult distribution and spawning ranges. Although the Saco River and estuary is the fourth largest water- way system in Maine, this ecosystem has remained relatively unstudied over the last thirty years, and research describing the temporal ichthyoplankton composition and distribution is virtually absent. The present study examined the structure of the ichthyoplankton community and determined the temporal and spatial variation in species diversity and abundance within the Saco Bay estuary system. Weekly sam- pling trips during the months of June, July, and August in 2007 revealed ten species of ichthyoplankton present in the study area. Ulvaria subbifurcata (Radiated Shanny) and Tautogolabrus adsperus (Cunner) dominated the abundance data followed by Hippoglossoides platessoides (American Plaice) and Myoxocephalus octodecims- pinosus (Longhorn Sculpin).

Sediment transport and dispersion in a cool-temperate estuary and embayment, Saco River estuary, Maine, USA

The Saco River flows through a rock bound, mid-latitude estuary recognized as the primary source of sand to the Saco Bay barrier beach system. To better constrain the conditions under which the Saco River contributes sand to Saco Bay, three moorings equipped with current meters and a CTD were deployed inside and outside the Saco River jetty system, from April to June, 2005. These measurements characterized high-discharge events and their competence for transporting sand outside the jetty system. Discharge values from 125–175 m 3 s − 1 were identified as the threshold envelope at which the Saco River transports sand in its bedload to Saco Bay. Put in an 89-year historical context with USGS stream gauge data, the Saco River is expected to contribute sand annually to the embayment, but the amount of transport varies significantly from year to year. The moored hydrographic data were augmented by geophysical, Langrangian drifter data, and local wind observations to better ascertain nearshore dispersal patterns once sand exits the jettied river mouth. These data suggest that transported sand responds to seasonably variable shelf conditions, reacts to artifacts of the jetty system, or exits Saco Bay. The results and methods of this study suggest that relatively small, rock-bound estuaries are potentially significant sources of sand to adjacent beach systems and the inner shelf, although the pathway for sand from river to shoreface to beach or inner shelf is complex and mediated by local meteorological and oceanographic conditions.

Sand budgets at geological, historical and contemporary time scales for a developed beach system, Saco Bay, Maine, USA

Saco Bay hosts one of the largest sand beach and salt marsh systems in northern New England, USA. Unsuccessful remedies for chronic beach erosion have generated controversy and differing theories regarding (1) the source(s) of sand to the bay, (2) the sand transport paths and (3) the role of jetties in beach erosion. We constructed a sand budget for the bay by evaluating the past and present sand-transport pathways, fluxes and reservoir volumes. Side-scan sonar and bottom samples were employed to map the offshore areas; seismic reflection profiles and vibracores were used to measure the volume of offshore sand. On land, ground-penetrating radar and cores constrained the sand volume and stratigraphy. Time-series maps and aerial photographs provided data on historical sand movement, and current meters and recent harbor dredge data allowed contemporary sand movement to be estimated in the Saco River estuary. At the present time, 56 million m 3 of sand reside in the shoreface and 22 million m 3 of sand are beneath the barrier beach and dunes. The Saco River has been the major source of sand to the bay, providing an estimated 10,000–16,000 m 3 of sand per year. The net direction of sand movement is to the north, where river-derived sand has historically fed growth of barrier spits. Construction of the north jetty at the Saco River mouth profoundly altered the prehistoric patterns of sand movement and storage in the bay, causing the northward migration of almost 6 million m 3 of sand between 1867 and 1955. Contemporary dredging of tidal inlets involves sand volumes approximately equal to the influx of sand delivered by the Saco River.