The Sedimentation Impact for the Lagoon and Mangrove Stabilization

Sedimentation causes land accretion, silting river water, lagoon, and mangrove degradation. The current study aims to analyze the potential and the impact of sedimentation toward the potential of the lagoon and mangrove ecosystem in Segara Anakan Lagoon. The research methods used mapping analysis, total suspended solid analysis (TSS), sedimentation rate analysis, biodiversity analysis, and mangrove covering. The result showed that (1) the value of TSS between 0.25-1,16 g L-1 (2) sediment flux between 6,8 257,7 g m-2s-1 (3) annual rate of sedimentation in West Segara Anakan Lagoon (W-SAL) between 13.82 – 15.49 m yr-1. (4) The effects of sedimentation were (a) the remaining lagoon of West Segara Anakan Lagoon (WSAL) which was 1.200 ha, (b) land accretion in W-SAL between 27.24 – 160.18 m (1994 – 2003) and 20.91 – 107.55 m (2003 2014), (c) the remaining mangrove of SAL less than 2594 ha (d) the mangrove diversity ranged between 0.48 – 1.71 (low – moderate), (e) the mangrove density of trees were 46 205 trees ha-1 (degraded) (5) mangrove landscape was developed to reduce the impact of sedimentation, especially the first zone of mangrove landscaping was dominated by Aegiceras Floridum, Avicennia Alba, Avicennia Marina, Sonneratia Caseolaris, and Sonneratia alba.

Sedimentation process as a trigger factor of sustainability ecosystem in W-SAL occurred by transporting and depositing, the accumulated plastics, geochemical and sediment pollutants from the uplands, rivers, oceanic sources [24], [25], tide, and sea level [26], [27] and unstable hydrology [24], [28]. [29] explain the potential of sedimentation between 0.3 Mm3 y-1 within a period of 1927-1970 to 0.8 Mm3 yr-1 within a period of 1970-2002, and the possibility of sediment flux in the lagoon is 257, .7 g m-2s-1 (rainy season) and 6.8 g m-2s-1 (dry season) [11] will cause mangrove and lagoon degradation Many researchers also state that the sediment flux is a sedimentation indicator in W-SAL, which influences aquatic organisms' habitat, lagoon, and mangrove ecosystem [30]. The negative impacts of sedimentation in the lagoon ecosystem are decreasing of mangrove diversity and density, lagoon degradation, organisms death, land accretion and deposition [9], [31], the disturbance of ecological resilience [32], mangrove dying, and stunting [22].
The mangrove landscape in the sedimentary lagoon can reduce the impact of the sedimentation in the lagoon [11], [33], [34]. The mangrove landscape is designed to support the conservation mangrove and lagoon ecosystems [4], [35], [36]. In the aspect of research novelty, this study showed the correlation between the sedimentation potential and the species adaptation to reduce the impact of sedimentation, and develop the stabilization of the mangrove and lagoon ecosystem. This paper aims to analyze the impact of the sedimentation toward the lagoon and mangrove ecosystems by using variables of mangrove adaptation, mangrove biodiversity, and mangrove covering.

Research Procedures and Data Analysis The Sedimentation Potential
The Potential of sedimentation was measured by the sedimentation rate and the potential TSS in the lagoon. The first indicator is sedimentation rate.
The sedimentation potential was analyzed by using a sediment trapped method (g cm -2 day -1 ) with the following equation [11]: Notes: LS : The rate of the sedimentation (g cm -2 day -1 ) B : The dry weight of the sediment (g) : 3,14 R : The radius of the sediment trap (cm) The second indicator is Total Suspended Solid (TSS). The potential of TSS was collected by analyzing and observing the sediment load within 24 hours with intervals of 3 hours on River Citanduy. The potential of TSS data was taken during the peak tides in both the dry and rainy seasons.

The Sedimentation Impacts
The impacts of the sedimentation were analyzed by lagoon degradation-land accretion and the mangrove covering-the mangrove diverse density. The first indicator is lagoon degradation which used the mapping method with ARC GIS 10.3 software of 1994, 2003, and 2014. The mapping was used to analyze the shoreline change annual rate. The result of the shoreline annual rate was used to develop a prediction model. The shoreline annual rate model is built by the trendline method using shoreline change (Y variable) and year (X variable). Whereas land accretion is analyzed by seeing the difference between shoreline (i) and shoreline (i-1) The second indicator is mangrove density and diversity. Mangrove density in the sedimentary lagoon used the mangrove trees with system-based quadratic transects by the following equation: The species richness was categorized into (1) low (Dmg < 1), (2) moderate (Dmg score 1-3), and (3) high (Dmg >3) [23], [35], [42], [43].
(b) Heterogeneity. Heterogeneity showed the number of species in mangrove ecosystem with Shannon Wiener index [23], [35], [42], [43] The research study located in the Java Sea waters at longitude 106° East -116° East and latitude 3° East -7° East. The data used for this study encompass monthly average data of chlorophyll-a level 3 from Aqua MODIS satellite images with a resolution of 4 km [10] for 11 years taken from 2008 to 2018. Chlorophyll-a data processed using ArcGIS 10.3 software combined with Microsoft Excel for data processing and interpretation of chlorophyll-a changes over time using images and spatial distribution. The chlorophylla distribution map was generated and used for fishing ground analysis to predict the potential area of capture fisheries for the fisherman based on space and time.

Mangrove Landscape
The mangrove landscape is developed to draw mangrove zone, which functioned to reduce the sedimentation impacts. The mangrove landscape uses the parameters of mangrove covering, domination, and density in the sedimentary lagoon. This mangrove landscaping shows the mangrove adaptation in the sedimentary lagoon.

Potential Sedimentation in W-SAL
Potential sedimentation in W-SAL is shown by the potential TSS and annual rate of sedimentation. The first indicator was the TSS scores in the sedimentary lagoon ( Figure 2). The data showed that TSS in the bottom lagoon was more significant than the middle and water surface. [46] states that the factors of suspended material to deposit in the lagoon are substrate physical structures, such as particle volume, shape and scuttling, density, and porosity.
The data also showed that the highest TSS score on the rainy season reached 1.16 g L-1, and the lowest TSS score on the dry season was 0.75 g L-1. This data was not different from that obtained from [50], showing that the TTS score on the rainy season was 1.11 g L-1. [47] also state that the average TSS concentration in the estuary samples was 117.6 -6.2 mg L-1 with the highest TSS concentration by Nudgee Creek (134.4 -21.8 mg L-1) and the lowest concentration by River Mololah (90.71 -14.8 mg L-1) Meanwhile, the annual rate of sedimentation on the sedimentary lagoon as an indicator is shown in Figure 3. The potential of the annual rate showed the sedimentation fluctuation trend with the sedimentation potential and the flux sediment. The potential sedimentation between < 1 gr day-1 -110 g m-2day-1 and the sediment flux score in the rainy season was 257.7 g m-2s-1, while in the dry season it reached 6.8 g m-2s-1. The data from [11] shows that the sedimentation potential in W-SAL from River Citanduy was 7.4 million tons year-1 and deposited in the lagoon reaching 0.8 million tons year-1. [11], [48] also estimate that the sediment flux in W-SAL has reached 9.14 million tons year-1 and deposited until 0.66 million tons year-1, or 7% of the sediment to deposit into the lagoon ecosystem ( Figure 3). The data of CRMP (1992) notes that sediment supply from rivers to SAL was between 5.24 -12,7 million ton year-1, and 3,04 million ton year-1 (58%) of sediment supply from Citanduy river.  The lagoon degradation in W-SAL for 13 years reached 232 ha, or the lagoon degradation rate reached 17.8 ha per year-1. The lagoon degradation was caused by disposed of polluted substrates [49], which impact the narrowing and superficiality of the lagoon [50], the high of TSS, and the sediment disposal, [11] estimating that the total supply of mud to sedimentary lagoon reached 5.24 million m3 year-1. The sediment supply and transport from Citanduy River reached 3.04 million tons or 58% of the sediments total supply, Cibeureum river (0.01 million m3 year-1), Cikonde river until 2.19 million m3 year-1. In 1987, the water depth in W-SAL was 40 m, and it became 10 m in 2017. For now, the water depth in W-SAL only reaches 1.5 -2 m. The second indicator is the dynamic trend of the shoreline and is presented in Figure 5. The dynamics trend of the shoreline showed that the annual trends were 6.21 - The shoreline dynamics in W-SAL were influenced by the sediment transportation (bedload and suspended load), disposal activities, and inlet-outlet system from many rivers and the Indian Ocean [51]. [50] The water debit between 0-1200 m3 s-1 will supply the total suspended solid by 20.88 kg s-1 and the sediment flux by 0.0139 kg m-2s-1. [11] The sediment flux in the rainy season (March 2014) was 257.7 g m-2s-1, while in the dry season (August 2014) was 6.8 g m-2s-1. The sediment flux potential will increase the sediment load in Segara Anakan Lagoon between 9.14 -11.10 106 tons y-1 [11]. [52] It is predicted that in 2040 the supply of sediment load from Citanduy River will be 8,050,000 tons y-1, Cimeneng River will be 870,000 tons y-1, and Cikonde River will be 220,000 tons y-1. This condition may impact the sedimentation potential in Segara Anakan Lagoon to reach 5.24 -9.14 million tons y-1. The shoreline change in W-SAL had negative impacts on lagoon stabilization [50], [11] write that the sedimentation cause lagoon degradation in Segara Anakan from 6,450 ha (1944) to 1,043 ha (2016). The last indicator is the land accretion. It is shown in Table 2 and Figure 6. Based on 27 years of data, it was shown that the land accretion will be 1004.9 ha (49.1)%, or the land accretion rate in SAL will reach 40,20 ha year-1. The prediction model of land accretion was -1.3682 x2 + 62 x + 301.13 (R² = 0.9144) This model also predicted that the decreasing lagoon in Segara Anakan reached 784.13 ha (2026) and 993.13 ha (2046). [53] reported that the increasing land accretion in Segara Anakan Lagoon reached 1,004.9 ha or the sedimentation rate between 9.14 -11.10 million tons year-1. The mangrove degradation is shown by the degradation area and the mangrove density. The first indicator is the degradation area of the mangrove ecosystem is shown in Table 3 and Figure 7. The data showed the degradation area of mangrove ecosystem in Segara Anakan from 7.776 ha (1974) to 2.605 ha (2018), the rate of mangrove degradation in W-SAL reached 118 ha year-1, remaining mangrove area less than 2594 ha, and the model prediction was y = 7137e-0.022x (R² = 0.9324) The model predicted that the mangrove ecosystem potential in Segara Anakan was less than 1168.4 ha. The degradation area of the mangrove ecosystem is expressed by mangrove stunting, mangrove death [22], [32], and expansion of the associate species like Acanthus spp, Derris Trifoliata, Melaleuca Leucadendron, Heriteria Litoralis, Cytrus spp, Aegiceras Floridum, and Aegiceras Corniculatum [22], [23]. The second indicators were the degradation of mangrove density and diversity [44], [54]. This degradation is shown in Table 4. The data showed that the mangrove density in W-SAL only had 774 -1589 trees ha-1 (sapling and poles) and 81 -163 trees ha-1 (trees), the species abundance (Shanon Wiener) in W-SAL ranged between 0.47 (low) -1.85 (moderate) and species richness index (Margaleff index) ranged between 0.29 (low) -2.07 (moderate). This data indicated that mangrove in SAL was degraded. However, the mangrove diversity in W-SAL is still bigger than in Puerto Princesa Bay, Palawan Island, Philippines (having the Shannon index between 0.349 -0.912) [55] but lower than that in Kepulauan Meranti district [9], [15]. The data showed that the sedimentation might impact the selection of mangrove species to survive and live in W-SAL. [35], [56], [57].    Table 4 also showed that the number of mangrove species in W-SAL was 20 species which was bigger than mangrove ecosystems in Andaman and Nicobar Islands, India (15 mangrove species) [58], [59].

Mangrove landscaping to reduce the impact of sedimentation
The mangrove landscaping was developed by using species adaptation and mangrove covering (Table 5 and Figure 8) to reduce the sedimentary impacts. The species adaptation is shown by the area surrounding mangrove species.
The mangrove covering also represents the mangrove adaptation in reducing the sedimentation impacts [6] and the mangrove ability in doing respiration process in sedimentary lagoon [3], [6].

Figure 8. The Landscaping of mangrove ecosystem in W-SAL
Based on the sedimentation impact, the mangrove landscaping in W-SAL was zone 1 had Aegiceras Floridum, Avicennia Alba, and Marina, Sonneratia Alba, and Caseolaris. Zone 2 had Aegiceras corniculatum, Bruguiera gymnorrhiza, Nypa frutican and Rhizophora apiculata. Zone 3 had Ceriops Tagal, Rhizophora Mucronata, and Xylocarpus Spp. Zone 4 had Bruguiera sexangula, Ceriops decandra and exoecaria agallocha. The mangroves have good adaptation to reduce the sedimentation impacts and support the trapping directly, stabilize sediments, and reduce the substrate hydrodynamic exposure by the root systems [61], [62]. The best mangrove species to grow in this sedimentary lagoon are Sonneratia Caseolaris and Avicennia Marina. Sonneratia Caseolaris and Avicennia Marina have high adaptation to the root system (the area covering between 16-26%). The root system of these species can reduce the sedimentation impacts and grow in deep muddy soils using respiration metabolism and salt excluder metabolism. in West Segara Anakan Lagoon (W-SAL) (remaining is 1.200 ha), mangrove degradation (remaining 2.594 ha), and land accretion reach 784 -1004.9 ha. The mangrove landscaping must be well developed to reduce sedimentation. The mangrove landscaping showed that the first zone of mangrove landscaping in the sedimentary lagoon had Aegiceras Floridum, Avicennia Alba, Avicennia Marina, Sonneratia Caseolaris, and Sonneratia Alba.